Clinical Hematology

Disorders of Hemostasisand Thrombosis Vascular disorders ¡ö

Describe the physiology of the destruction and consumption of

¡ö

De? ne the term purpura and describe various vascular conditions

coagulation factors, including the role of factor VIII, protein C, and that can produce this condition. thrombin in the process of ? brinolysis. Abnormal platelet morphology ¡ö Compare the laboratory test results in conditions of disseminated intravascular coagulation (DIC) and ? brinolysis. ¡ö

Name and compare four types of disorders in which abnormal

¡ö

Name and describe the factors that contribute to the pathological

platelet morphology can be observed. inhibition of coagulation. Quantitative platelet disorders The hypercoagulable state ¡ö

Cite at least two symptoms of thrombocytopenia.

¡ö

Explain the role of vascular damage and blood ? ow in the hyperco-

¡ö

List the three major mechanisms that produce thrombocytopenias.

agulable state. ¡ö

Summarize the major characteristics of each of the three thrombo-

¡ö

Detail how platelets contribute to hypercoagulation.

cytopenic categories, including examples of disorders within each ¡ö

Describe the activity of blood coagulation factors in increasing the

of the categories or subcategories. tendency toward thrombosis. ¡ö

List and summarize the characteristics of the two categories of

¡ö

Describe the relationship between impaired ?

thrombocytosis, including each

examples

C, antithrombin III, and plasminogen.

of

disorders

within

¡ö

Describe the laboratory assessments that illustrate the condition of

Qualitative characteristics of platelets: hypercoagulation. thrombocytopathy Case studies ¡ö

Compare the four categories of platelet dysfunctions, including

¡ö

Apply the laboratory data to the stated case studies and discuss the

examples of disorders within each category. implications of these cases to the study of hematology. Bleeding disorders related to blood clotting factors ¡ö

Give examples and describe conditions that contribute to the defec-

tive production of blood coagulation factors. VASCULAR DISORDERS Bacterial toxins produce de-endothelialization induced by Disorders of the microcirculation, platelets, may cause abnormal bleeding. Abnormal the loss of red blood cells from the itself as the condition of by hemorrhages into the skin, internal organs. Purpura may be produced vascular abnormalities. These abnormalities include the

or plasma proteins purpura, mucous by

which a

is

variety of

following:

an endotoxin. Antibody vascular injury, vasculitis, may be induced by drug reactions, insect bites, or the activation of complement. 2. Purpura associated with an inherited disease of the connective tissue. Alterations of the vascular ve framework can occur in disorders such as diabetes. 3. Purpura associated with decreased mechanical strength of the microcirculation. Decreased strength can be seen in conditions such as scurvy and amyloidosis. 1. Purpura associated with direct endothelial cell damage. 4. Purpura associated with mechanical disruption of small The overall action of endothelins, a family of peptides, is venules. The principal cause of this type of purpura is to increase blood pressure and vascular tone. Endothelial

supporti

increased intraluminal pressure. This condition can be damage may result from physical or chemical injury to observed around the ankles with prolonged standing and the tissue caused by microbial agents such as in rickettmay be caused by the presence of abnormal proteins in sial disease or immunological antibody-mediated injury. macroglobulinemias or hyperviscosity disorders. PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

5. Purpura associated with microthrombi (small clots). This lation (DIC), type of disorder is associated with abnormal intravascular myocardial infarction, and ischemic injury to the legs or coagulation conditions. arms¡ªcan produce severe morbidity and mortality. Serum 6.

Purpura associated with vascular malignancy. Purpura of this

from patients with HIT contains immunoglobulin G (IgG) origin is observed in Kaposi sarcoma and vascular that, in the presence of small amounts of heparin, activates normal platelets and causes them to aggregate and release the contents of their granules, including serotonin. PlateABNORMAL PLATELET MORPHOLOGY let-activating antibodies are speci? c not but for complexes formed between heparin and platelet factor

for

heparin

the

with hep

When examining a peripheral blood smear for platelets, the morphology of the platelets should be observed. Abnormal variations in size should be noted. Disorders of platelet size include the following: 4, a heparin-binding protein normally found in the alphagranules of platelets. IgG and IgM also react with endothelial cells coated with platelet factor 4 (Fig. 24.1). This suggests a mechanism of antibody-mediated vascular injury that could predispose a patient to thrombosis or DIC when challenged 1. Wiskott-Aldrich syndrome, which demonstrates arin. To prevent these complications, it has become

smallest platelets seen medical

practice

platelet

counts in

2. May-Hegglin anomaly, which is characterized by the in for any extended period.

patients receiving hepar

presence of large platelets and the presence of D?hle-like Most thrombocytopenic conditions can be classi? bodies (see Chapter 15) in the granulocytic leukocytes major categories. These categories are 3. Alport syndrome, a disorder that exhibits giant platelets and thrombocytopenia 4. Bernard-Soulier syndrome, which demonstrates the largest platelets seen and is also referred to as giant platelet syndrome. In this disorder, it has been demonstrated that the giant platelets are probably an artifact of the slide 1. Disorders of production destruction, including decreased megakaryocytopoiesis and ineffective platelet production, and disorders of utilization 3. Disorders of platelet distribution and dilution preparation. Actual measurement of the platelets reveals that their mean platelet volume (MPV) is normal Disorders of Production Decreased production of platelets may be caused by hypoproliferation of the megakaryocytic cell line or ineffective thrombopoiesis caused by acquired conditions or herediQUANTITATIVE PLATELET DISORDERS frequently affects other

normal cell

lines

of

the

bone

marrow and

The normal range of circulating platelets is 150 ¡Á 10 /L to hypoproliferation 450 ¡Á 10 /L. When the quantity of platelets decreases to can

result from

acquired

damage to

hematopoietic

levels below this range, a condition of thrombocytopenia of the bone marrow caused by factors such as irradiation, exists. If the quantity of platelets increases, thrombocytosis

cells

drugs (e.g., chloramphenicol and chemotherapeutic agents), is the result. Disorders of platelets can be classi? chemicals (e.g., insecticides), and alcohol. In? tative (thrombocytopenia or thrombocytosis) or qualitative bone marrow by malignant cells in the conditions of meta(thrombocytopathy). static cancer, leukemia, and Hodgkin disease can produce a hypoproliferative state. Hypoproliferation may also result Thrombocytopenia from nonmalignant conditions, such as infections, erythematosus, granulomatous disease such as sarcoidosis,

lupus

A correlation exists between severe thrombocytopenia and and idiopathic causes. spontaneous absent or

clinical

bleeding.

If

platelets

are

Ineffective thrombopoiesis may result in decreased platelet severely decreased below 100 ¡Á 10 /L, clinical symptoms usuproduction. Thrombocytopenias of this type may be the manially include the presence of petechiae or purpura. Petechiae festation of a nutritional disorder, such as a de? appear as small, purplish hemorrhagic spots on the skin or or folic acid. In these megaloblastic anemias caused by mucous membranes; purpura is characterized by extensive or folic acid, the defect in thymidine areas of red or dark-purple discoloration. Thrombocytopenia can result from a wide variety of or ineffective thrombopoiesis. Another disorder related to inefconditions, such as after the use of extracorporeal circulafective thrombopoiesis is iron de? tion in cardiac bypass surgery or in alcoholic liver disease. decrease in megakaryocyte

and the suppresHeparin-induced thrombocytopenia (HIT) and associated endoproliferation and size. Hereditary thrombotic events, relatively common side effects of hepathrombocytopenias include Fanconi syndrome, constitutional rin therapy, can cause substantial morbidity and mortality. aplastic anemia and its variants, ameiosis thrombocytopenia Thrombocytopenia in itself rarely poses a threat to affected (TAR syndrome), X-linked amegakaryocytic thrombocytopepatients, but nia, Wiskott-Aldrich deep

disorders syndrome,

venous thrombosis,

associated May-Hegglin

with it¡ªwhich anomaly, and

disseminated intravascular coagu-

syndrome). Formation of PF4¨Cheparin complexes IgG antibody Heparin-like molecules vessel wall Formation of immune complexes (PF4¨Cheparin¨CIgG) PF4 release Disorders of Destruction or Utilization Increased destruction or utilization of platelets may result from a number of mechanisms. Destruction Caused by Immune Mechanisms, Antigens, activation Antibodies, or Complement Drugs or foreign substances can produce platelet destruction. FC receptor

include

These

drugs

include

quinidine,

sulfonamide

derivatives,

venom. Sulfonamide derivative reactions involve the interaction of platelet antigens with FIGURE 24.1. Proposed explanation for the of both thrombocytopenia and thrombosis in heparin-sensitive patients

presence

drug antibodies. Morphine reactions involve the activation of complement. who are treated with heparin. Researchers believe that injected heparin reacts with platelet factor 4 (PF4) that is normally Bacterial Sepsis Bacterial sepsis causes increased s ties from complexes

destruction

of

platelet

circulating platelets to form PF4-heparin because of the attachment of platelets to bacterial antigen¨C

Speci? c IgG antibodies react with these conjugates to form immune complexes.

Certain microbial

antigens

(2) that bond to Fc receptors on circulating attach initially to platelets followed by antibodFc-mediated from

platelet

activation

(3)

releases

ies to the microorganism. This mechanism has been reported alpha- granules in platelets (4). Newly released PF4 binds to addiimmune complexes, establishing a cycle of platelet activation. PF4 released in excess of the amount that can be neutralized by available heparin binds to heparin-like molecules (glycosaminoglycans) on the surface of endothelial cells (ECs) to provide targets for antibody binding. This to cause the thrombocytopenia that frequently complicates the Plasmodium falciparum type of malaria. Thrombocytopenia occurs within 1 to 3 weeks following viral infections (e.g., rubella, mumps, or chickenpox), parasitic or bacterial infections, or hepatitis vaccination. process leads to immune-mediated EC injury (5) and heightens the risk of thrombosis and disseminated intravascular coagulation. (Adapted with permission from Aster RH. Heparin-induced Immune thrombocytopenia Antibodies of either autoimmune or isoimmune origin may thrombocytopenia and thrombosis, N Engl J Med, 332(20):1375,

PF4

produce increased destruction of platelets. An example of an 1995. Copyright 1995 Massachusetts Medical Society. All rights autoimmune

thrombocytopenia

is

autoimmune reserved.) thrombocytopenia. This condition occurs in infants born PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

to mothers with chronic immune thrombocytopenia following least 30% of thrombocytopenic patients develop venous transplacental passage of maternal IgG platelet and/or arterial thrombosis. Examples of thrombocytopenias of isoimmune origin The lowest platelet counts range between 20 and 150 ¡Á include posttransfusion purpura and isoimmune neonaabout 5 tal thrombocytopenia. Posttransfusion purpura is the onset of the declining platelet count. The platelet count

a

rare

the

platelet

form of isoimmune thrombocytopenia. Isoimmune neodays after heparin therapy natal thrombocytopenia results from the immunization of normal within 4 a pregnant female by a fetal platelet antigen. The antigen cases, it can take is inherited by the fetus from the father and is absent on disappears within maternal platelets. 2 to 3 months after discontinuing heparin administration. Thrombocytopenia in pregnancy Thrombosis

occurs in

most

patients

count diminishes by 30% to 50% of the normal level. The

after

Pregnant women generally have lower platelet counts than risk of thrombosis persists for up to 30 days after discontinunonpregnant women. Gestational thrombocytopenia rin. Rare cases of thrombosis have been reported

is

ing hepa

caused by a combination of d before the platelet count declines.

and

increase

platelet activation of approxi-

and

hemodilution

clearance.

A

decrease

A rare manifestation of delayed-onset HIT has been observed. mately 10% in the platelet count is typical toward the end of In these cases, thrombocytopenia began at least 5 days after disthe third trimester of pregnancy. Bleeding is uncommon. Heparin-Induced Thrombocytopenia Pathophysiology HIT is the most common drug-induced thrombocytopeImmune HIT is caused by an antibody that recognizes heparin nia. HIT and antiphospholipid syndrome (APS) are two bound to platelet factor 4 (PF4) on the platelet which

antibodies

against

antibody then

binds

to

complexes tal

of

charged

the

heparin-PF4

complex,

molecules

are

which of

fundamen

allows the antibody to bind the Fc receptor on the platelet. importance. In the case of APS, the antibodies are autoantiInteraction with the Fc receptor activates the platelet that bodies compared to the drug-induced antibodies of HIT. In results in the loss of platelets, thrombocytopenia, and platelet both syndromes, IgG antibodies directed against positively aggregation (thrombosis). A small number of cases of HIT charged (GP I)

endogenous

proteins,

b2

glycoprotein

I

may involve an antigen other than the PF4 complex. in APS and platelet factor 4 (PF4) in HIT, are of major importance. Laboratory Data HIT is a serious complication of heparin therapy. This In addition to the platelet count, three speci? c laboratory condition is also called ¡°white clot syndrome¡± because it assays can be used in patients with HIT: poses a high risk of potentially catastrophic venous or arterial thrombosis. The mortality rate of patients with thrombosis is approximately 25%. Thrombocytopenia and thrombosis are the predominant 1. Enzyme-linked immunosorbent assay (ELISA) 2. Platelet aggregation 3. Serotonin release clinical symptoms of HIT. The ELISA assay and serotonin release assay have sensitivities Two types of HIT exist of more than 90%, with very high speci? city for HIT anti1. Nonimmune HIT: Type I 2. Immune HIT: Type II body. Platelet aggregation is between 50% and 80% and is very speci? c. Increased Utilization of Platelets Nonimmune Heparin-Induced Thrombocytopenia Accelerated

consumption

of

platelets

is

Nonimmune HIT is a benign disorder affecting up to 10% the

most

important

and

frequently encountered forms of increased consumption mechanism of action is direct interaction between heparin of platelets is immune (idiopathic) thrombocytopenic purpura and platelets. This antibody-related response, which

another cause

Typically, the platelet count is greater than 100.00 ¡Á 10 infection, is believed devastating effect Although a rapid decline is observed within the ? on platelet survival. ITP may complicate other antibodyheparin administration, the platelet count returns to normal associated disorders such as systemic lupus erythematosus levels within 5 days despite continued heparin use or within immunological

thrombocytopenic

2 days if heparin therapy is discontinued. petechiae, bruising, Immune Heparin-Induced Thrombocytopenia rhagia, and bleeding after minor trauma. Approximately 8% of patients who receive heparin therapy Immune Thrombocytopenia develop HIT antibody but do not experience thrombocytopeimmune thrombonia. Another 1% to 5% of patients receiving heparin therapy cytopenia (ITP), to the term, idiopathic thrombodo develop HIT antibody and manifest cytopenic purpura. an acquired immune-mediated CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

In ion

ITP,

the

acute is

mechanism

of

platelet

suggested to be either by absorption of viral antigen onto the platelet surface followed by antibody binding or by formation of an immune complex on the surface of platelets via the platelet Fc (immunoglobulin) receptors. In chronic

destruct

ITP, the target for the autoantiplatelet antibodies is platelet membrane and

GPs

(e.g., GPIIb/IIIa,

GPIb/IX,

GPIa/IIa,

GPIV). The majority of platelet autoantigens are present on either GPIIb/IIIa or GPIb/IX complex. The mechanism of autoantibody formation is unknown. Laboratory Data Isolated ity.

thrombocytopenia

is

the

essential

Diagnosis requires exclusion of other causes of thrombocytopenia. Antibodies to speci? c platelet-membrane GPs can be detected in most patients, but neither these assays nor disorder characterized by isolated thrombocytopenia ( count < 100 ¡Á 10 /L) and the absence of any obvious initiating and/or underlying cause of the thrombocytopenia. ITP occurs in children and adults and is characterized by a low platelet count, normal bone marrow, and the absence of measurements of platelet IgG, which are often erroneously referred to as antiplatelet-antibody tests, are important for the diagnosis or management. The American Society of Hematology has established the following guidelines for the diagnosis of ITP: other causes of thrombocytopenia. Various characteristics Presence of thrombocytopenia, lack of anemia exist in ITP (Table 24.1). loss has occurred, and lack of white abnormalities Absence of other causes of thrombocytopenias (e.g., Epidemiology vascular diseases or lymphoproliferative disorders) ITP is a fairly rare, generally benign illness in the pediatric 3. Absence of infections, particularly human immunode? population. About two thirds of children recover spontaneciency virus (HIV) ously. In adults, the incidence is approximately equal for both

abnormal

genders except in the mid-adult years (30 to 60 years), when Treatment the disorder is more prevalent in women. ITP is classi? Platelet time

transfusions

are

seldom indicated.

Survival

duration into newly diagnosed, persistent (3 to 12 months of transfused platelets is short, but they are important for controlling

severe hemorrhage.

The

ef?

Typically, adult ITP is a chronic disease. ITP in children may improve immediately after an infusion of intravenous is a clinically distinct disorder and is usually acute. Among immune globulin.

Intravenous

immune globulin

is

an

are

unusual.

adults, ITP is most common in young women (approxiimportant agent in managing acute bleeding and in preparmately 70% of patients are 10 to 40 years old). Chronic ITP ing for procedures, such as delivery. Treatment of pregnant is a destructive thrombocytopenia caused by an autoantiwomen with ITP is a complex problem. body. Approximately 80% of patients experience remisSplenectomy was a well-recognized treatment for ITP for sions after either corticosteroid therapy or splenectomy. more than 30 years before glucocorticoids were introduced in Some patients respond to other therapy; in a substantial 1950, and its success in achieving complete responses in two group of patients, the disease is refractory to therapy. thirds of patients has been remarkably consistent for more Clinical Signs and Symptoms than 60 years. A response to splenectomy typically occurs within several days; responses after 10 days Onset is gingival

often

insidious.

Purpura,

epistaxis,

and

When treatment is considered for patients with more severe bleeding are common. Hematuria and gastrointestinal bleedthrombocytopenia the

and

symptoms,

it

must

be

with

ing are less common, and intracerebral hemorrhage is rare. understanding that complete and permanent correction of Serious bleeding does not occur in most patients. thrombocytopenia is infrequent with any therapy. Pathophysiology The old concept was that thrombocytopenia resulted from antibody-mediated platelet destruction. There are two new concepts: Thrombocytopenia Intravascular coagulation, vascular injury or occlusion, andtissue injury can al l contribute to the increased utilization of platelets. DIC rapidly consumes platelets. Trauma, obstetrical 1.

The same antibodies that mediate platelet destruction also

examples of disorders mediate impaired platelet production by damaging megaconsumption of platelets. In karyocytes and/or blocking their ability to release proplatethe case of bacterial sepsis, thrombin-induced platelet aggrelets. T cell¨Cmediated effects are believed to play a role gation in vivo contributes to the thrombocytopenia. 2. Ten to twenty percent of cases are not antibody mediated platelets because of PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

the direct consumption of platelets at the sites of endothelial Disorders of Platelet Distribution loss without appreciable depletion of clotting factors such as brinogen. A platelet distribution disorder can result from a pooling of platelets in the spleen, which is frequent if splenomegaly Thrombotic Thrombocytopenic Purpura

is present. This type of thrombocytopenia develops when more than a double or triple increase in platelet producThrombotic thrombocytopenic purpura (TTP) is a clinical tion is required to maintain the normal quantity of circusyndrome with a high mortality rate that is characterized by lating platelets. Disorders that may produce splenomegaly formation of microthrombi in the microvasculature. with resultant splenic pooling or delayed intrasplenic transit Clinical signs and symptoms include include alcoholic or posthepatic cirrhosis with portal hyper¡ö ¡ö

Severe thrombocytopenia Microangiopathic hemolytic anemia

tension, lymphomas and leukemias, and lipid disorders such as Gaucher disease. ¡ö ¡ö

Fever Neurologic symptoms, for example, headache, stroke

Thrombocytosis ¡ö

Renal disease

Thrombocytosis is generally de? ned as a substantial increase The

hematological

findings

of

thrombocytopenia

in circulating platelets over the normal upper limit of 450 ¡Á red blood cell schistocytes are diagnostic of the disease. 10 /L. Thrombocytosis can be classi? Coagulation testing will demonstrate normal prothrombin and activated partial thromboplastin time (aPTT) but elevated D-dimer and fibrinogen levels. TTP is in contrast to DIC that demonstrates abnormal prothrombin time (PT) and aPTT. Three types of TTP have been identi? ed 1. Hereditary or familial thrombocytosis associated with germline mutations of the thrombopoietin (THPO) gene in the THPO receptor (MPL) gene 2. Thrombocytosis associated with myeloproliferative neoplasms and/or myelodysplastic disorders (clonal 1. Idiopathic thrombocytosis associated with somatic mutations of

and

2. Secondary JAK2[V617F], MPL, and additional currently unknown 3. Inherited (Upshaw-Shulman) Idiopathic has been

TTP

has

an

unknown

etiology

but

3. Reactive (secondary thrombocytosis) linked to an enzyme, ADAMTS13 (A Disintegrin-like And Many patients with thrombocytosis have reactive thromMetalloprotease domain with ive thrombocytosis may be observed in

ThromboSpondin-type

bocytosis. React

motifs), responsible for the breakdown of large von Willea variety of disorders and conditions, including chronic brand

factor (vWF)

multimers.

High¨Cmolecular-weight

blood loss, chronic inflammatory diseases, chronic infecvWF in the plasma of patients with TTP promotes the tions, drugs, asplenic states and splenectomy, malignanaggregation of platelets in vivo, which produces most of cies,

rebound

thrombocytosis following

treatment

of

the clinical symptoms. immunological

thrombocytopenic

purpura,

pernicious

Secondary TTP is diagnosed in patients with a history of anemia, discontinuance of myelosuppressive drugs, acute medications, for example, quinine, immunosuppressants, or blood loss, exercise, and myelodysplastic and hemolytic some cytotoxins used in cancer therapy. This form of TTP anemias. After splenectomy, increases are noted because has been seen in some conditions, for example, HIV, autoimof the loss of the spleen. As the bone marrow adjusts to mune disorders, and allogeneic bone marrow transplants. new requirements, platelet numbers progressively return Upshaw-Shulman syndrome

accounts

for

5%

to

10%

to normal. of cases. It is the result of inheritance of a deficiency of Because of a poorly understood mechanism of stimulaADAMTS13. This milder form of TTP is manifested in tion associated with the hemolytic process, thrombocytosis childhood

when

there

is

increased

vWF,

for

example,

may also be seen in autoimmune hemolytic anemia. inflammation. Another disorder, hemolytic uremic syndrome (HUS) is a clinical syndrome with presentation and manifestations similar to TTP. Unlike TTP, which has a peak age incidence in the third decade, HUS has a peak incidence QUALITATIVE CHARACTERISTICS OF PLATELETS:THROMBOCYTOPATHY between 6 months and 4 years of age. Unlike TTP, HUS is characterized by If platelets are normal in number but fail to perform effectively, a platelet dysfunction exists. In addition to both an ¡ö of

Association with Escherichia coli O 157:H7 in individual and family medical history, laboratory tests are

platelet ¡ö

dysfunctional

diagnosis.

80%

Renal failure and limited to the kidneys

tests of platelet function include bleeding time, ¡ö

Small vWF multimers predominate

clot ness,

retraction,

¡ö

Normal level of ADAMTS13 activity

platelet

aggregation,

platelet

adhesive

and antiplatelet antibody CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

Myeloproliferative Syndromes Acquired in the

platelet

dysfunction

is

commonly

myeloproliferative syndromes. Platelet aggregation patterns

seen

are often not characteristic and could represent any combination of platelet aggregation defects. Uremia is commonly accompanied by bleeding caused by platelet dysfunction. It is proposed that circulating guanidinosuccinic acid or hydroxy phenolic acid interferes with platelet function. Dialysis often corrects or improves platelet function. Other mechanisms of altered platelet function in uremia, including altered prostaglandin metabolism, have been proposed. Paraprotein Disorders Paraprotein disorders including malignant or benign such as multiple myeloma, Waldenstr?m other monoclonal gammopathies, Types of Platelet Dysfunctions Dysfunction results from the paraprotein coating the platelet membranes but does not depend on the type of paraprotein Three separate categories of platelet dysfunctions can be idened based on etiology (Table 24.2). These include the more common acquired causes and the less frequent hereditary present. Almost all patients with malignant paraprotein disorders will demonstrate clinically signi? mal platelet function by aggregation. causes. Disorders within these categories can be identi? using speci? lets associated with hypercoagulability and thrombosis make up an additional category of abnormal platelet function. Cardiopulmonary Bypass and Platelet Function These conditions demonstrate severe platelet function de? cit that assumes major importance in surgical bleeding after Acquired Acquired platelet function defects can be caused by a blood plasma inhibitory substance. Examples of disorders or diseases that may exhibit this dysfunction include infused dextran, uremia, liver disease, and pernicious anemia. Laboratory testing reveals the presence of ? brinolytic degradation or split products (discussed later in this chapter). The most common acquired platelet defects are summarized in Table 24.4. Many patients with these platelet function disorders, who are candidates for surgery, may bleed profusely as a result of surgery or from trauma.

Miscellaneous Disorders Associated With Platelet Dysfunction Acquired defects are seen in autoimmune disorders, such as SLE, rheumatoid arthritis (RA), ITP, and scleroderma. Fibrinogen degradation products or ? brinogen split products (FDPs or FSPs) including the later degradation products, fragments D and E, have a high af? brane and produce a severe platelet function defect. Patients with severe iron, folate, or cobalamin de? ciency may also have platelet function defects. Acquired Platelet Function Defects penicillin, and alcohol. In addition, prostaglandin pathways inhibited and

by

aspirin,

cyclosporine

(Sandimmune,

ibuprofen,

Neural,

hydrocortisone,

NOVARTIS,

Basel,

Switzerland). The arachidonic acid platelet aggregation assay is the only practical way to monitor the effects of aspirin therapy, now widely used to prevent stroke and heart attacks. Hereditary Hereditary platelet dysfunctions are caused by an inherited platelet defect that is either structural or biochemical (Table 24.5). Examples of adhesion disorders include Bernard-Soulier syndrome,

a

collagen

receptor

Glanzmann thrombasthenia, and storage granule abnormalities. Secondary aggregation disorders include hereditary

storage pool

defect and

hereditary

aspirin-like

Also included among hereditary disorders are defects of connective tissue, such as collagen, and failure of platelets to adhere to the subendothelium because of a decrease or defect in plasma coagulation factors. An example of a defect of platelet plug formation owing to decreased platelet adhesion to the subendothelium is von Willebrand disease (see discussion later in this chapter).

defect,

Bernard-Soulier Syndrome Bernard-Soulier syndrome,

an

autosomal

hereditary

ing disorder, is a platelet adhesion disorder in which platelet membrane GPs Ib, V, and IX are missing. Heterozygotes are often asymptomatic. The condition is characterized by the presence of giant platelets. In this syndrome, there is mild thrombocytopenia, but the predominant abnormality is of the CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

membrane GP Ib. This abnormal platelet membrane lacks the platelet function defects. In instances, receptor site for vWF, which is necessary for platelets to adhere storage pool defects are to vascular subendothelium. A blood ? syndrome, Bernard-Soulier syndrome may resemble that from a patient syndrome, Ch¨¦diak-Higashi with ITP. Platelet aggregation is normal with all agents except syndrome.

Clinical

features

aggregation ristocetin. Clinical features include easy bruising, epistaxis, mucocutaneous hemorrhages and hematuria, hypermenorrhagia, and petechiae (Table 24.6). Petechiae are Glanzmann Thrombasthenia and Essential Athrombia less common than in other qualitative platelet disorders. Hereditary aspirin-like defects are a rarer form of secondGlanzmann thrombasthenia and essential athrombia are similar, ary aggregation defect. Clinical features are similar to other

bleed-

rare, primary aggregation disorders. Glanzmann thrombasplatelet function defects. thenia is an autosomal recessive disorder. Clinical features Storage granule abnormalities, primarily an absence of the involve platelet dysfunction, easy and spontaneous bruising, dense granules, exist in conjunction with other clinical dissubcutaneous

hematomas,

and

petechiae.

Intra-articular

orders, such as Ch¨¦diak-Higashi syndrome, Wiskott- Aldrich bleeding with hemarthrosis may occur in some patients but and Hermansky-Pudlak syndrome. In these

syndrome,

tends to diminish with age. disorders, platelet aggregation with weaker agents, such as This disorder involves an abnormality of the surface memADP and epinephrine, is diminished. brane GP complex IIb/IIIa. On a peripheral blood ? lm, platelets from patients with this disorder remain isolated and do not exhibit the clumping that is normally seen. Epinephrine, collagen, and thrombin fail to induce aggregation. This results in a prolonged bleeding time in the presence of a normal platelet BLEEDING DISORDERS RELATED TO BLOODCLOTTING count, decreased platelet retention in glass bead columns, and an absence of a primary wave of aggregation in response to adenosine diphosphate (ADP). Clot retraction is also decreased. Vascular response and platelet plug formation are responsible for the initial phases of hemostasis. Subsequent to these activities, the clotting factors are initiated to form the ? Hereditary Storage Pool Defect clot. Fibrin formation can occur if the activity of various factors is at least 30% to 40% of normal. Hereditary aggrega-

storage

pool

defect is

a

secondary

hereditary

storage pool

Bleeding and defective frequently tion s

disorder.

Overall,

disorder

related to a coagulation factor. Disorders of the blood coagulaare more common than primary aggregation disorders of tion factors (Table 24.7) can be grouped into three PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis Defective Excessive inhibition

production destruction

Hemophilia Etiology Hemophilia has been used as a paradigm for understanding Defective Production the molecular pathological processes that underlie hereditary disease. The cloning of factor VIII facilitated the identiVitamin K De? A condition of defective production may be related to a de? ciency of vitamin K. The synthesis of vitamin K and dependent factors can be disrupted because of disease or drug therapy (e.g., cephalosporin antibiotics). Vitamin de? ciencies are also encountered in neonates, malabsorption syndrome, biliary obstruction, and patients taking oral anticoagulants. Vitamin K depletion develops within 2 weeks if both intake and endogenous production are eliminated. Factors II, VII, IX, and X are vitamin K dependent. Factor VII has the shortest half-life and usually declines in the early stages of vitamin K depletion. A mild de? cation of mutations that lead to hemophilia A, an inherited ciency of factor VIII coagulant activity that causes severe hemorrhage. Two types of mutations dominate the defects identi? ed so far: gene deletions and point mutations. Gene deletions are associated with severe hemophilia A in which no factor VIII circulates in the blood. To date, approximately 50 deletion mutations in the gene for factor VIII have been characterized at the molecular level, and 34 independent deletion mutations in the factor IX gene have been found to be the cause of hemophilia B. Point mutations, in which a single base in DNA is mutated to another base, represent a second type of mutation that causes hemophilia. may present as an asymptomatic prolongation of a patient¡¯s Epidemiology PT assay. Individuals with hereditary clotting defects may be either Severe Liver Disease genetically homozygous or heterozygous carriers of the trait.

K

The level of factor activity ranges from 0% to 25% in persons Because the liver is the primary site of synthesis of coagulation homozygous for the trait and from 15% to 100% in persons factor, severe liver disease can cause defective production of heterozygous for the trait. Defects of this origin may result coagulation factors. Severe liver disease may produce decreased from the decreased production of a clotting factor, factor plasma levels of ? brinogen, although low levels of ? brinogen VIII, or the production of functionally inactive molecules of rarely produce hemorrhage. In patients with liver disease, the the clotting factor. Hemophilia A, a sex-linked homozygous PT is noticeably prolonged, whereas the aPTTs are variable. disorder expressed in males, occurs in 1 in 10,000 males. Hereditary Clotting Defects Pathophysiology Classic hemophilia

(hemophilia

A)

and

von

Willebrand

Classic hemophiliacs have an intact high¨Cmolecular-weight disease are examples of hereditary disorders that represent moiety and a de? cient low¨Cmolecular-weight procoagulant functionally inactive factor VIII. portion. This disorder of procoagulant synthesis expresses CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

Von Willebrand Disease In 1926, Erik von Willebrand ? rst described a hemorrhagic disorder characterized by a prolonged bleeding time and an autosomal inheritance pattern that distinguished the from classic hemophilias. In the early 1950s, an additional component VIII

of

procoagulant

the activity

disease was

identi? ed: a de? ciency of

(Table 24.8). These

other observations distinguish von Willebrand disease from

and

classic factor VIII:C de? ciency (hemophilia A). In addition, evaluation of the multimeric structures of vWF has aided in the classi? cation of the variant forms of von Willebrand disease. Three major types of von Willebrand disease have been identi? ed. Etiology von Willebrand disease may d

be

an

acquired

or

The congenital disorder is autosomally dominant in most cases. Inherited abnormalities in von Willebrand disease are associated with a defect of the vWF gene on chromosome 12, but in some patients, the coexistence of an impaired response of plasminogen activator and telangiectasia suggests the presence of a regular defect or more extensive endothelial abnormalities. In several families, a large vWF gene deletion has been identi? ed as the basis for von More than 20 distinct clinical and laboratory subtypes of von Willebrand disease have been described (Table 24.9). Three

broad

types

of

von Willebrand disease are

nized. In addition, a platelet-type von Willebrand disease (pseudo¨Cvon Willebrand disease) is caused by an abnormal platelet receptor for vWF. In addition, acquired von cation of von Willebrand Disease (continued ) Willebrand disease may complicate other diseases such as the

primary

lymphoproliferative and autoimmune disorders, and prosynthesis and release of plasma vWF; the other type of cell degradation

of

synthesizes vWF is Approximately

vWF

complicates

myeloprolifera-

recog-

inherite

tive disorders. Variant forms of von Willebrand disease can produced in the megakaryocyte. identi? ed by their patterns of genetic transmission and vWF circulates in platelets, being stored primarily in the alpha the vWF abnormalities in the plasma and the cellular comgranules, in association with factor VIII procoagulant protein partment. Distinguishing between various subtypes of von released from the alpha granules important in determining appropriate the GP IIb/ therapy (Table 24.10). IIIa complex. The site synthesis of VIII:Ag remains unknown, Epidemiology although the liver is thought to play an important role. vWF is a large, adhesive, multimeric GP present in plasma, von Willebrand disease is recognized as one of the most platelets, and subendoth elium. It is synthesized as a large common hereditary bleeding disorders in humans. The exact precursor that consists of a signal peptide, a propeptide (von cult to determine because milder forms are has the two often not clinically recognized, but it has been estimated to (VIII:C) and have a prevalence as high as 1% in the general population. subendothelial cell No racial or ethnic predisposition has been determined. circulating blood, vWF is Both genders are affected, but there is a higher frequency of with the factor VIII clinical manifestation in women. stabilizes

Pathophysiology and protects it from rapid removal from the circulation. The vWF portion represents more than 95% of the mass of the von Willebrand disease is characterized by abnormal platecontrols the molecular stereochemislet function, expressed as a prolonged bleeding time. This is The vWF consists of repeating multimers, with the smalla consistent ? nding and may be accompanied by decreased dimer or tetramer. factor VIII procoagulant activity. Circulating

vWF

undergoes

proteolytic

cleavage

vWF circulates in the blood in two distinct compartments, can be distinguished from with two types of cells being responsible for vWF producplatelet vWF, is not proteolyzed. The pathogenesis of CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

von Willebrand disease is based on quantitative or qualitahomozygous type I (or compound heterozygous) tive abnormalities, or both, of vWF. When an abnormality and type III disease is present, the decreased factor VIII procoagulant activity is is unclear but is characterized decreased circulating levattributable to the reduced concentration of vWF. decreased proportionally with vWF is essential in providing the basis for formation of a respect to vWF. c sites on the

under

Most patients with von Willebrand disease (50% or more) platelet, namely GP Ib and GP IIb/IIIa, while concurrently abnormalities and no evidence binding to the subendothelium of damaged walls, tional abnormality of vWF, which corresponds to type I von forming of vWF,

vessel

a bridge. Patients with decreased levels Willebrand disease and its subtypes. The genetic transmis-

especially the larger multimeric forms, will lack adequate sion of the disease is dominant, except possibly for subtype bridging action that produces prolonged bleeding times. I-3. Most patients have low plasma levels of vWF antigen Qualitative or quantitative abnormalities of vWF result in (usually between 5% and 30% of normal) and corresponddecreased bleeding activity

adhesion ingly low (the assay

and are levels of

responsible ristocetin

for the cofactor

associated with von Willebrand disease. of vWF to GP Ib and mediate The signi? cance of vWF in the regulation VIII:C platelet agglutination). The factor VIII procoagulant protein

of

remains unclear. The increase in VIII:C following infusion of the decrease in vWF. ed vWF suggests a possible role of vWF in the syntheinsuf? cient levels sis, release, or stabilization of VIII:Ag. Therefore, decreased circulating vWF and factor VIII. Bleeding manifestations are levels of vWF may prolong the rate of blood clotting. in patients who have normal concentration of Clinical Signs and Symptoms platelet vWF than in others (Table 24.11). The

severity

of

symptoms

among

patients

with

von Willebrand disease varies greatly. Severe cases are not easily distinguishable clinically from severe hemophilia A, in which bleeding occurs into the joints and fascial planes. Characteristically, in patients with von Willebrand disease, the bleeding is mucosal in origin, with epistaxis, menorrhagia, and gastrointestinal bleeding being the most common. Bleeding associated with surgical procedures and oral surgery is a particular problem. Homozygous patients may experience severe bleeding, including hemarthrosis, or potentially lethal gastrointestinal tract or central nervous system hemorrhage. cation of von Willebrand Disease Type nd

I

is

the

most

common variant of

von

disease and appears to be based on a quantitative de? ciency of vWF. It is expressed as an autosomal dominant trait and is presumed to be caused by an inheritance of one normal cient allele. Patients with severe type III disease PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

In all patients whose vWF shows low ristocetin cofactor phenomena. vWF may be an indicator of vascular activity, except for those designated as having type B disease, status. Drugs such as 1-deamino-8-D-arginine vasopressin the vWF has an abnormal multimeric structure and there is (DDAVP), steroids, and hormones may also result in elevated a decrease in or absence of the large multimers. levels of vWF. Type II is characterized by structurally abnormal vWF. The circulating levels of vWF may be decreased or normal, Laboratory Findings and VIII:C may be affected similarly. Type IIA and type IIB

Willebra

The following laboratory results are typical of von are autosomally dominant, whereas type IIC is recessive. Patients with type III, the most severe form of von Willebrand disease, are likely to have a major episode of bleeding early in life because signi? cantly decreased amounts of vWF and VIII:C are produced. Genetically, they are thought to be homozygous or double heterozygous. These patients probably comprise a separate group because of the typically ¡ö ¡ö ¡ö ¡ö ¡ö

Bleeding time: mildly to moderately prolonged Platelet retention: typically decreased Platelet agglutination: ristocetin¡ªabnormal Platelet aggregation: normal with all but ristocetin vWF function (ristocetin cofactor activity)

recessive modality of genetic transmission (Table 24.12). Quantitation of vWF antigen (vWF:Ag) can be determined by Acquired von Willebrand Disease immunoelectrophoresis. These assays measure total amounts of vWF protein, independent of its ability to function. Finally, von Willebrand disease is occasionally seen as an acquired vWF multimeric analysis is useful in distinguishing between condition. Associations have been made with lupus erythesubtypes and in determining therapeutic management. vWF matosus and other autoimmune disorders as well as myeloanalysis

uses

sodium dodecyl sulphate

proliferative disorders. The presence of a circulating antibody agarose gel

electrophoresis and

radiolabeled

antibody

to vWF may be implicated in some cases. Another mechathe different molecular weight multimers. nism responsible for decreased amounts of vWF in acquired states is the absorption of the coagulation component onto Other Hereditary De? abnormal cell surfaces. Hemorrhagic complications are genas hemophilia B or Christerally more severe in patients with acquired von Willebrand This

form

non¨Csex disease. Bleeding from mucous membranes is more common and occurs at a of 1/50,000 in the general population, and re? ects the much lower levels of vWF activity in these molecule being the usual cause. It individuals. vWF activity is typically 20% or less of normal. cally indistinguishable from hemophilia A and must be difPseudo¨Cvon Willebrand Disease ferentiated by laboratory testing. A de? ciency of factor XI is referred to as hemophilia C. This genetic defect is an autoThis is a rare disorder in which patients resemble those with trait that occurs almost exclusively in people von Willebrand disease because of low levels or absence of mild disorder characterized large multimeric forms of vWF in the plasma. Patients with epistaxis, and hemorrhage in conjunction pseudo¨Cvon Willebrand disease have a platelet abnormality with trauma. The laboratory results in this defect, as well in which spontaneous platelet aggregation occurs. Low levthose of other hemophilias and von els of larger multimers result from increased consumption presented in Table 24.13. during platelet aggregation. absent or Increased Levels of vWF decreased levels of ? brinogenemia, respectively.

? brinogen, a? brinogenemia, or Production of dysfunctional

Increased levels of vWF have been associated with stress, molecules produces dys? brinogenemia. A? brinogenemia is

hypo-

in? ammation, postsurgical states, pregnancy, renal disease, associated with a severe bleeding tendency but is less common diabetes, rheumatoid disorders, scleroderma, and Raynaud than hypo? CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

are usually asymptomatic except in situations of surgery or apparent, and factor XIII de? ciency, associated brinogenemia may be asymptomwith spontaneous abortion and poor wound healing. atic or experience a mild bleeding tendency if heterozygous bleeding tendency if Disorders of Destruction and Consumption homozygous for the defect. ciencies of the other coagulation factors are brin deposits can result in thrombosis and damrelatively rare (Box 24.2). Examples of rare defects include ow and ischemia. The factor XII de? ciency, in which no clinical bleeding tendencies ? brinolytic system serves as a protective mechanism against brin deposits by lysing both ? Blood coagulation factors can be destroyed in vivo by enzymatic of

degradation

or

by

pathological

coagulation with excessive utilization of the clotting factors. Enzymatic destruction can result from bites by certain species of snakes whose venom contains an enzyme that degrades brin monomer. In vivo activation of coagulation by tissue thromboplastin¨Clike materials can produce excessive utilization of clotting factors. Conditions

activation

associated

with

this

consumption

of

coagulation

factors

include obstetrical complications, trauma, burns, prostatic and pelvic surgery, shock, advanced malignancy, septicemia, and intravascular hemolysis. General Features of Fibrinolysis Primary and secondary ?brinolysis are recognized as extreme complications of a variety of intravascular and extravascular disorders and may have life-threatening consequences. PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis ? brinolysis is associated with conditions in which

Other causes can include liver disease, lymphoproliferagross sub-

activation

of

the

? brinolytic

mechanism

with

tive disorders, and renal disease. In addition, DIC can also sequent

?

be triggered by trauma including shock, hypothermia, and occurs. The important characteristic of primary ? brinolyextensive tissue damage, such as in myocardial infarction sis is that no evidence of ? brin deposition occurs. Primary and eclampsia. It has been associated with multiple surgical, brinolysis occurs when large amounts of plasminogen actiobstetrical, and medical disorders. Coma and convulsions vator enter the circulatory system as a result of trauma, surcan result. gery, or malignancies. Although the same clinical conditions may also induce secondary ? brinolysis or DIC, the distinction between the two is essentially in the demonstration of ? brin formation. In secondary ? brinolysis, excessive clotting and ? brinolytic activity occur. Increased amounts of ? brin split (degradation) products (FSPs) and ? brin monomers are able because of the action of thrombin on the ? brinogen molecule. This ? clotting; therefore, it is a secondary condition. Distinguishing between primary and secondary ?

detect-

important in treatment. Pathophysiology The overall DIC process involves coagulation factors, platelets, vascular endothelial cells, ? This major breakdown of the hemostatic mechanism occurs when the procoagulant factors outweigh the anticoagulant mechanisms. Initiation of DIC can be caused by a number of factors. If vascular endothelial damage results in the exposure of collagen and basement membrane, collagen can activate factor XII. Factor XII has multiple roles in the direct or indirect activation of coagulation including Disseminated Intravascular Coagulation Initiation of the intrinsic clotting cascade resulting in Etiology thrombin formation DIC is actually a complication or intermediary phase ofmany diseases and does no t constitute a disorder in itself. cofactor for the conversion of prekallikrein to kallikrein It is also known as consumptive coagulopathy or de? 3. Initiation of ? nation syndrome. Triggering events that may predispose patients to DIC include alterations in the ium, direct activation of ? brinogen, release of thromboplastinlike substances, and erythrocyte or platelet ion. Extravascular trauma, abruptio placentae, advanced malignancy, leukemia, and retained fetal syndrome are examples of clinical situations in which tissue thromboplastin can activate coagulation. Infections, most commonly Gram-negative microorganisms, can trigger DIC by producing endotoxins that expose Regardless of the initiating event, DIC is characterized by excess thrombin formation, conversion of brin, and platelet consumption and deposition. Secondary ? brinolysis occurs as a result of ? brin deposition and can decrease plasma coagulation factors, leading to a diathesis. Thrombin is central to the mechanism of consumptive coagulopathy. The action of thrombin on the coagulation systems includes collagen. Stasis, shock, or tissue necrosis can have the same Proteolytic cleavage of brinogen to

?

endothel destruct

brin monomer, effect. Snakebites may introduce substances that initiate coagreleasing (? brin monomer may ulation by direct activation of ? form soluble complexes with ? blood cell or platelet injury may contribute to the consumpthrombi that entrap platelets during thrombus tive coagulopathy by releasing phospholipids that accelerate 2. Activation of factor XIII, which stabilizes ? coagulation. Red cell injury may be a result of intravascular hemolysis caused by malaria, incompatible transfusion 3. Stimulation of platelets, resulting in decreased circulating products, and other clinical states. Platelet destruction also platelets. These stimulated platelets undergo shape change, releases coagulation factors V, VIII, XII, and XIII. adhesion, aggregation, and secretion. The contents of the CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

dense alpha-granules are released, leading to an acquired mechanisms are ciency. If, during perhaps a 3-hour span, process.

Coagulation

factors

brinogen levels decrease signi? cantly rapidly

than

they

in a critically ill patient, DIC should be the prime suspect be replaced, antithrombin III (AT-III) levels depleted, as the cause of this change

system cannot 4. Activation of factors V and VIII; however, thrombin actithe activated coagulation proteins. vation results in unstable end products that have decreased factor V and VIII activity Alternate Forms of DIC 5.

Activation of protein C, which degrades factors V and VIII

DIC

presents

forms

in

in

brinolytic system is suddenly actibrin thrombi in the vasculature, primarily In essence, it is a systemic pathobrinolysis. This secondary logical process. Because two involved, brinolysis is responsible for the hemorrhagic complication brinolytic system, several types of ed clinically: When the ? brinolytic system is activated, plasminogen is brinolytic 1.

DIC: Clotting and lysis strongly activated (most common

inhibitor uniquely designed to cope with plasmin. The more plasmin generated, the more alpha-2 antiplasmin the patient consumes. This produces a vicious cycle in which increased activation leads to decreased inhibitors; this, in turn, allows more increased activation to continue. This is known as a positive 2. DIC: Clotting predominates with little or no lysis (poor prognosis) 3. Primary ? brinogenolysis: Only lysis activated, but many coagulation factors consumed feedback loop and leads to a situation incompatible with life. clotting system and Damaged tissue, especially renal cells, releases plasminosystemigen activators that convert plasminogen to plasmin. Plasmin

brinogen is a proteolytic enzyme that destroys ? brin, ? brinogen, and most instances, the simultaneous generation of clotting factors V and VIII. Circulating plasmin may lead to plasmin will dissolve brin. Both the clotting and ? brinolysis, causing increased hemorrhagic events. performing at abnormally high In the microcirculation, plasmin¡¯s action is lysis does not occur, a different form of DIC exists. In this directed against ? brin. In the circulation, the breakdown of case, the prognosis is very type is represented ? brin results in FSPs, labeled X, Y, D, and E, which inhibit brinolythrombin and normal platelet function. brinogenolysis. Coagulation brinogen is degraded by plasmin, FSPs form. Degrathe excess plasmin being generated. dation occurs whether the plasmin comes from DIC or pribrinogen The Role of Factor VIII molecules for thrombin molecules. This competitive binding close relationship exists between factor VIII:C (procomakes the thrombin unavailable for the conversion of ? (procoagulant antigen). In DIC, brin. In this situation, patients with high FDP/FSP lesser extent levels have a circulating anticoagulant behaving like heparin. than VIII:C by enzymes released during the process. It is known If the FSP level is high, the thrombin clotting time is sig-

primarily

is destroyed by amounts of brinogen quantitation is low. The thrombin, plasmin, and activated protein C (aPC). second effect is on platelets. These split products coat the inactivation of platelet surface, blocking the receptor site needed for further the degree of severity platelet activation. DIC. Furthermore, low values of factors VIII:C and VIIIR:Ag When pathological ? brinolysis occurs, not only are facpatients with tors destroyed, but, through the destruction of ? brinogen, irreversible shock indicate clinical outcome. Discrepa profound anticlotting effect inhibits secondary hemostasis exist between VIII:C and VIIIR:Ag and platelets. ratios are brinolytic system is activated, it will contribute to of DIC. Current the consumption of many coagulation factors. Plasmin, the thinking indicates that data on the factor VIII complex show primary proteolytic enzyme of ? brinolysis, directly attacks characteristic decrease of the factor VIII and destroys them. This becomes another form of consumpin DIC formulated in the past is tive t

coagulopathy originating generally valid.

source with the same end result. When systemic clotting

from

an

activation

entirely

differen

begins, the

body

The Role of Protein C stop it. The two major inhibitor systems mechanism of hemoof coagulation are antithrombin and the protein C and S stasis. In addition, PC is now recognized as playing a systems. These inhibitors are consumed in the DIC process. and chronic in? ammatory PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

diseases, for example, sepsis or asthma. When in? ammamechanisms, the coagulation process tion occurs, coagulation is also set in motion and actively can return to normal. This negative feedback mechanism has participates in enhancing in? slow the formation of excess thrombin and PC is a vitamin K¨Cdependent serine protease that is

to stop DIC.

synthesized, predominantly in the liver, as a single polypeptide chain of 461 amino acids and is a natural antiClinical Signs and Symptoms coagulant protein. The conversion of PC to activated PC The DIC phenomenon has varied clinical and laboratory (aPC) is enhanced by interaction of PC with endothelial physiologiPC receptor (EPCR) on the cell surface. Activation can cal abnormalities associ ated with the syndrome. DIC may also be triggered by thrombin alone at a less ef? cient rate (chronic). Chronic DIC is more and is probably not relevant in the circulation. The funcDIC but is often more cult to diagnose. tion of aPC as an anticoagulant is manifested by its ability

to acute consumption if the to inactivate two important cofactors of the coagulation of procoagulant-anticoagulant is lost. cascade: factor V/Va and factor VIII/VIIIa. These eventsare enhanced by the pres ence of Ca , phospholipids, and cofactor protein S. initially be seen with varying degrees of thrombosis and hemorrhage, but bleeding is usually the major symptom, particularly in acute cases. Both hemorOther functions of aPC in hemostasis are in maintaining rhagic and thrombotic complications may accompany DIC, uid state of blood. aPC has the ability to downregulate often is

being

manifested

in

the

same

patient.

thrombin and suppress the activation of thrombin actimay predominate in chronic or low-grade DIC. Thrombotic vatable ? brinolytic inhibitor, which indirectly promotes complications can include deep venous thrombosis. ? brinolysis. Fibrinolysis is also stimulated because of the Acute DIC is severe and often life threatening. Its onset ability of aPC to inhibit plasminogen activator inhibitor-1 is rapid, and both ? (PAI-1). Patients with chronic DIC may have mild manifestations The induction of ? of the disorder or be recognizable only by laboratory data. tem may facilitate the clearance of excess thrombi and genHemorrhagic complications are also seen but are generally eration of FSPs. If aPC is being consumed too rapidly, the milder than in acute DIC. regulatory ability of the protein C system is sharply reduced, Clinical manifestations of DIC include petechiae, purpura, which results in uncontrollable thrombosis.

Thrombos

hemorrhagic

bullae,

surgical

wound

bleeding,

Thromboembolic complications occur in patients with wound line

bleeding,

venipuncture

site

bleeding,

arterial

hereditary de? ciencies of protein C (levels 60% or less of oozing, and subcutaneous hematomas. normal). als

Fatal

neonatal

purpura develops

in

individu

TTP is a condition that is similar to DIC (Tables 24.16 born with a homozygous protein C de? ciency. The stimuli and 24.17). In addition, pediatric respiratory distress synthat can induce DIC may ultimately result in abnormal levdrome (PRDS), adult respiratory distress syndrome (ARDS), els of protein C. Both normal and abnormal levels of protein HUS, preeclampsia or frank eclampsia, circulating immune C antigen can be found, depending on the sample time relacomplex,

cavernous

hemangiomas,

and

Rocky

Mountain

tive to the onset of DIC. Plasma levels of protein C antigen spotted fever can resemble DIC. and activity have been found to be decreased in patients with DIC. Whereas three fourths of DIC patients have a decrease in protein C antigen, almost all DIC patients have a decreased level of protein C activity. Monitoring patients reveals that protein C antigen and activity decrease progressively during the initial stages of DIC and remain at a low level for 24 to 48 hours before gradually returning toward normal in nonfatal cases. The Role of Thrombin Mechanisms on of

involved

in

DIC

result in

thrombin in the circulating blood. Among its many feedback

the

generati

reactions, thrombin participates indirectly in the activation of the ? brinolytic system secondary to DIC and activates protein C. The latter reaction is accelerated by the presence of the endothelial cell cofactor, protein S. In ng

addition its

to

cleaving

? brinogen

and

performi

other procoagulant functions, some of the excess thrombin binds to protein S on the endothelial cell surface. This event leads to increased levels of APC in the plasma. Once the generation of excess thrombin is decreased by the action of APC CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

Laboratory Findings AT-III have also been suggested to be of prognostic value. The Although the quantitative measurement of FSPs distinguish between primary and secondary ? brinolysis, such measurement plays the major role in diagnosing and monitoring these conditions. Laboratory diagnosis of DIC requires the availability of tests that are rapid and simple to perform. There is no single test that con? but rather a combination of tests. Because DIC is a dynamic process, values from tests performed a single time, whether normal or abnormal, cannot be used as diagnostic indicators. Sequential testing is necessary to provide an accurate diagnosis and effectively manage therapy. The most important consideration in the treatment of DIC is the resolution key feature is an elevation of Typical results in DIC include thrombin time and an increased levels and the total

circulating ? brinogen-FSPs. prolonged aPTT, PT, and level of D-dimers. platelet count may

vary,

decrease in ? brinogen are common. The platelet count decreases earlier than ? endotoxin-induced DIC. The reverse is true when tissue factor release is responsible, such as in obstetrical accidents or trauma. Excessive ? brinolysis with the release of FSPs occurs secondary to intravascular ? brin formation. Although presence of FSPs is characteristic, the ? DIC and cannot be used as the sole criterion for diagnosis. of the underlying disease or triggering event. Tests for Fibrinolysis and DIC Disorders Related to Elevated Fibrin SplitProducts Because the

manifestations of

?

cannot

although

the

extremely variable, diagnosis depends on laboratory testing. The normal level of serum FSPs is less than 10 mg/mL. Serum Coagulation assays such as the platelet count, ? values can vary owing to exercise or stress. Elevated urinary els, FSP test, factor V assay, ethanol gelation test, and thromlevels are always indicative of a disease state. High levels of bin time¨Creptilase test can all be useful. Prekallikrein and FSPs indicate renal dysfunction. Normal urinary FSP values PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

are generally less than 0.25 mg/mL but may rise to as high as 50 mg/mL in certain kidney disorders. Elevated levels of FSPs can be found in diseases of the neonate, in sepsis, or in the DIC that these conditions may generate. In cases of pulmonary embolism, levels can exceed 100 mg/mL; however, in rare cases, values can reach more than 400 mg/mL. These excessively high levels return to near normal within 24 hours after the cessation of the disorder (e.g., sepsis). FSP levels are elevated, frequently as high as 80 mg/mL, in cases of mild chronic intravascular coagulation, which occurs when the placenta slowly releases thromboplastic substances into the circulation. The FSP test can help distinguish between eclampsia and hypertension and edema associated with pregnancy. THE HYPERCOAGULABLE STATE Systemic in? ammation has long been recognized as being associated with hypercoagulability. It commonly occurs in patients with DIC in severe sepsis. Recently, the molecular ammation has been recognized. Most of the hypercoagulable effects of in? ammation are sis or occlusion in an unusual location such as a mesenteric, brachial, or cerebral vessel.

mediated by in? ammatory cytokines, including IL-1, IL-6 and tumor necrosis factor (TNF). The processes of coagulation, thrombosis, and in? ammaSecondary States of Hypercoagulability tion do not occur in isolation. There is interaction between Secondary hypercoagulation states may be seen in a numthese as

systems.

Thrombosis

and

coagulation

can

ber of heterogeneous disorders. In many of these conditions,

act

ammation, and severe or systemic in?ammaendothelial activation by cytokines leads to the loss of normal tory responses can trigger coagulation. A laboratory assay, vessel-wall anticoagulant surface functions, with conversion high-sensitivity C-reactive protein (hsCRP), may herald an to a proin? ammatory thrombogenic phenotype. Important impending acute thrombotic event. clinical syndromes associated with substantial thromboemThrombi may form because coagulation is enhanced or bolic events include the APS, heparin-induced thrombopabecause protective devices such as ? brinolysis are impaired. thy, myeloproliferative syndromes, and cancer. An increase in the likelihood of blood to clot is referred to as Hypercoagulability

can

be

associated

with

the hypercoagulable state. in? ammation due primarily to an increase in procoagulant Thrombosis is promoted by vascular damage, by retarded functions, an inhibition of ? brinolysis, and a downregulaow, and by alterations in the blood that increase the tion of the three major physiologic anticoagulant systems of likelihood of clotting. A variety of high- and low-incidence protein C, AT-III, and tissue factor inhibitor.

systemic

disorders are associated with thrombosis (Box 24.3). A number of factors may contribute to hypercoagulation. Pregnancy-Associated Thrombosis Primary States of Hypercoagulability Normal pregnancy beginning at the time of conception is associated with increased concentrations of coagulation facHypercoagulable states include

various

inherited

and

tors VII, VIII, and X and von Willebrand factor. In addition, acquired increased

clinical

disorders

characterized

by

an

a signi? cant change in ? brinogen is noted. Free protein S, risk for thromboembolism. Primary hypercoagulable states the active, unbound form, is decreased during pregnancy. (Table 24.18) include ns

relatively

rare

inherited

Plasminogen are

inhibitor

type

1

activator

conditio

(PAI-1) levels

that lead to disordered endothelial cell thromboregulation. vefold. PAI-2 produced by the placenta increases These

conditions

include

decreased

thrombomodulin-

signi? cantly during the third trimester. Thrombin generadependent activation of APC, impaired heparin binding of tion markers, for example, prothrombin F1+2, and thromAT-III, or downregulation of membrane-associated plasmin bin-antithrombin (TAT) complexes are also increased. It may generation. take up to 8 weeks after delivery (postpartum) for the levels The major inherited inhibitor disease states include ATof the cited constituents to return to the reference range. ciency, and protein S de? Pregnant women have an increased risk of thromboemboThese

conditions

should be

considered

in

patients

who lism due to hypercoagulability. The condition of hypercoaguhave recurrent, familial, or juvenile deep venous thrombolability in pregnancy is most likely evolved to protect women CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

against the bleeding challenges of childbirth or miscarriage. ow at critical sites with the accumulation of Pregnant women are at a four- to ? vefold increased risk of activated clotting factors. thromboembolism during pregnancy and the postpartum period compared to nonpregnant women. Eighty percent of Platelets the thromboembolic events in pregnancy are venous with an Stasis makes easier for

platelets

detached

from

to

incidence of 0.49 to 1.72 per 1,000 pregnancies. circulating Risk factors for developing hypercoagulability include platelets may tendency toward thrombosis. Platelets ¡ö History of thrombosis ¡ö Inherited and acquired thrombophilia ¡ö Maternal age less than 35 years of age ¡ö Certain medical conditions and/or complications of pregnancy and childbirth accumulate at the site of vascular damage, where they can phospholipid for the intrinsic pathway and also promote thrombin formation by adsorbing activated factor X from plasma to their surfaces. High platelet counts additionally foster thrombosis. Another possibility is that a thrombotic tendency may be caused by qualitative alterations in platelets. These alteraGeneral Features tions may be caused by intrinsic platelet defects or by changes

in the surrounding plasma. Qualitative abnormalities may Vascular Damage and Blood Flow result in spontaneous aggregation, enhanced sensitivity to Vascular endothelial damage exposes circulating blood to aggregating agents, or increased adhesiveness. subendothelial structures that initiate thrombosis. Constriction of blood vessels additionally creates stasis. Thrombosis ow or in situations in which the viscosity of blood is increased. In patients with a high risk of thrombosis, the concentration of ? brinogen is often elebrinogen may induce aggregation of circulating erythrocytes, which produces increased blood viscosity. This may encourage thrombosis by decreasBlood Clotting Factors Congenital and acquired hypercoagulable states arise when there is an imbalance between the anticoagulant and prothrombotic activities of plasma in which the prothrombotic activities predominate. A tendency toward thrombophilia (abnormal thrombosis) may be caused by qualitative alterations in blood PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

factors or an increased titer of activated clotting factors that limitations the

inherent

aPTT-based

can create a tendency toward thrombosis. These factors can method, which requires a and may contribute to thrombosis in that activated might be affected by high concentrations of factor VIII, LA, and reach critical levels in the circulating blood. anticoagulant therapy. The DRWT also eliminates the techFactor V (Leiden) nical requirement of prediluted patient samples with factor cient plasma. The factor V gene is an autosomal, codominantly inherited gene. Factor V R506Q (Leiden) mutation is the most com-

factors

Genetic Testing mon underlying genetic cause of thrombophilia (e.g., venous Single-nucleotide polymorphisms (SNPs) are major contribthrombosis). utors to genetic variation, comprising approximately 80% Factor V G-A point

(Leiden) mutation results from a of all known polymorphisms. Their density in the human

-Gly substitution in the proestimated per

1,000

base

tein. This mutation renders factor V resistant to the activity pairs. APC-resistant patients may be con? rmed for factor V of APC and induces a defect in the natural anticoagulation cation of a segment system. The overall effect of this mutation is an alteration in of the potentially affected gene. General population screenthe anticoagulant properties of factor V. ing is not recommended. At this point, the recommendations Factor V,

like

thrombin,

possesses

both

anticoagulant

for testing focus primarily on individuals younger than age and procoagulant properties. The APC-mediated cleavages, 50 who have already had an idiopathic thrombotic event. if performed on factor V, transform it into an APC cofacThe three most common assays ordered to investigate a tor (FVac). FVac acts in unison with APC and protein S to genetic predisposition to thrombosis are increase the rate of inactivation of factor VIII. In contrast to other coagulopathies, factor V poses a lifelong risk of deep venous thrombosis with a greater frequency of occurrence of thrombi in the lower limbs than 1. Factor V (Leiden) mutation

(Leiden)

3. Methylenetetrahydrofolate reductase enzyme (MTHFR) in the chest. Fortunately, everyone who has the mutation an increased risk will not suffer a thrombotic event. Heterozygotes have a low vascular thrombosis. MTHFR de? ciency leads (approximately 10%) lifetime to hyperhomocysteinemia that

risk, may

but homozygotes can injure the vascular

experience a 50- to 100-fold increase in risk. endothelium. It role in venous thromboemboLaboratory Assessment lism. These three assays can be performed simultaneously by analyzing genomic DNA in peripheral blood mononuclear A panel of assays is required to assess hypercoagulability. cells using polymerase chain reaction (PCR). Functional screening tests include the following: Circulating Anticoagulants ¡ö Activate and partial thromboplastin time (aPTT) ¡ö Lupus anticoagulant (LA) screening brinogen (factor I) assays ¡ö APC assay ¡ö Protein C and protein S assays ¡ö D-dimer screening test Acquired inhibitors of clotting proteins, also known as circulating anticoagulants, inactivate or inhibit the usual procoagulant activity of coagulation factors. Inhibitors are frequently c, those directed against a coagulation factor, or nonspeci? c, those directed against a complex of factors, such as the LA. The majority of these inhibitors exhibit biochemical propIn addition, acute-phase reactants (e.g., C-reactive protein erties, suggesting that they are immunoglobulins. Inhibitors [CRP]) may be assayed. may or

arise in

following

transfusion

of

blood

Traditionally, the APC resistance assay identi? es patient patients with no previous hemostatic disorders. Acquired

products

insensitivity to APC. The assay is based on the aPTT assay cant cause of hemorrhage. with and without reagent APC. The aPTT in the presence of Speci? c inhibitors against factors II, V, VII, VIII, IX, XII, XIII, and vWF have been detected in patients with individto yield a unitless ratio. A ratio of greater than 2 (a longer ual factor de? ciencies. However, some inhibitors of factors clotting time) generally indicates an unaffected condition. II, V, VII, IX, XII, and vWF have been observed in patients A ratio of less than 2 (a shorter clotting time) indicates a having no de? ciencies of coagulation factors. Patients with potential factor V (Leiden) mutation and resistance to APC. acquired speci? c inhibitors may exhibit hemorrhagic epiFactor V¨Cde? cient plasma may be added to the test system c inhibitors are not generally associencies. The APC resisciated with bleeding tendencies. tance assay may be affected by other conditions (e.g., LA, brinogen levels, oral contraceptive Etiology use, or pregnancy). The incidence of circulating anticoagulants has been benchAnother method of testing for the mutation is by a dilute marked population,

but

certain

Russell¡¯s viper venom time (DRVVT) based test. The DRWT patient

populations

have

higher incidence inhibitor CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

development. Inhibitors, found in both serum and plasma, platelet poor and free of are not inactivated by heating at 56¡ãC for 30 minutes and remain stable when stored at ¨C20¡ãC. Inhibitors are more comparison, anticardiolipin antibodies (ACAs), IgM, stable than clotting factors and more tolerant of changes in the phospholipids pH and temperature. Inhibitors may remain in the circulaof beta 2-GP 1-cardiolipin comtion for months and in some instances have been found in may be detected in healthy patients and in those with patients years after development. of conditions (e.g., SLE). c Inhibitors LA and ACA are risk factors for thrombosis but the mechanism of action is unclear. Antiphospholipid Antibodies (Lupus Anticoagulant and Anticardiolipin Antibodies) Antiphospholipid Syndrome The lupus anticoagulant (LA) occurs in approximately 30% to40% of patients with SLE. LA is the most common coagulaThe APS is de? ned by the persistent presence of antiphospholipid antibodies. APS is a prothrombotic disorder with tion inhibitor found in SLE patients, although these patients various manifestations in patients with a history of recurmay have other acquired inhibitors as well. LA occurs in the rent venous or arterial thromboembolism or a history of presence of disease states other than SLE, such as acquired miscarriages. APS is an important cause of acquired thromimmunode? ciency syndrome (AIDS) and malignancy, and bophilia. APS can occur alone or in association with other in procainamide, hydralazine, or chlorpromazine therapy.

autoimmune conditions, particularly SLE. The core clinical Although LA is rarely

exhibits

an

anticoagulant

effect, it

manifestation is thrombosis. In women, it can be associated associated with bleeding. with recurrent fetal loss. Fetal morbidity and mortality may LA, an IgM, IgG, or IgA immunoglobulin, interferes with be due to factors such as placental thrombosis and placental phospholipid-dependent coagulation reactions in laboratory ammation due to complement activation. assays but does not inhibit the activity of any speci? c coaguAntiphospholipid antibodies include lation factor. LA is an inhibitor that prolongs phospholipiddependent clotting tests in vitro. LA is the most common cause of prolonged aPTT. In 1995, the Subcommittee on Lupus Anticoagulant Standardization Committee published criteria (Box for the diagnosis of LA. This guideline recommends at least two screening tests based on different assay principles. In addition, a mixing study for the veri? cation of the presence of a coagulation inhibitor and a con? rmation test for documentation of phospholipids dependency should also be performed. All assays should be performed on citrate

24.4)

¡ö Anticardiolipin antibodies ¡ö Anti-b2-glycoprotien-1 antibodies. In the laboratory, elevated levels of antibody are required to establish a diagnosis. The predominant antigenic targets in APS are b 2-GP I and prothrombin. Complement activation is suspected because increased complement activation products have been found in APS patients who have suffered from a cerebral ischemic event. Dysregulated platelet activation may contribute to thrombotic manifestations. Elevated levels of platelet-derived thromboxane metabolic breakdown products have been demonstrated in the urine of APS patients. Factor VIII Inhibitor Factor VIII inhibitors are the most common speci? c factor inhibitors. Inhibitors of factor VIII develop in 10% to 15% of patients with factor VIII de? ciency (hemophilia A), and

the majority occur in patients with severe hemophilia (those having less than 1% factor VIII activity). Inhibitors have developed in patients exposed to factor VIII after as few as 10-exposure

days

but

may

develop after

several hundred

days. Approximately 65% of patients with hemophilia who develop inhibitors do so before the age of 20. Nonhemophiliac women have been reported to develop factor VIII inhibitors during the the

postpartum

period,

most

frequently

after

birth of their ? rst child. Patients with underlying immunological disorders such as RA, SLE, drug allergies, ulcerative colitis, and bronchial asthma also have an increased tendency to develop factor VIII inhibitors. Many patients have been observed to develop factor VIII inhibitors with no underlying disease. The majority of these patients are middle aged or older, and both genders are affected. PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

Inhibitors

against vWF

Nonhemophiliac patients inhibitors

occur

in

patients

with

of

Willebrand disease, underlying diseases such as malignancy major bleeding requiring transfusion. or SLE, and in previously healthy persons. A familial tendency Patients with inhibitors to factor XI, and factor XII for the development of vWF inhibitors has been noted. However, Factor IX Inhibitor therapy for these patients can be complicated by the

with

von

of the inhibitor. Patients with acquired factor IX inhibitors Inhibitors are found in approximately 2% to 3% of factor patients with IX¨Cde? cient (hemophilia B) patients, but the incidence of inhibitors. Factor V inhibitors may cause clinical bleeding, inhibitors in severe hemophilia B may be as high as 12%. although

the

degree of

hemorrhage

Although of

these

inhibitors

are

varies considerably.

predominantly

a

result

Inhibitors of factors XIII, II, VII, IX, and X; ? transfusion of blood products, spontaneous inhibitor forgen can result in serious hemorrhagic events. mation has been reported. Laboratory Findings Factor V Inhibitor Prolonged findings.

PT

or

aPTT

are

classic

laboratory

Factor V inhibitors are rare and are not generally associated plasma with

normal plasma at

with hereditary factor V de? ciency. Some patients have had 37¡ãC

(mixing study) and

determination

of

aPTT

and

exposure to streptomycin but no causal relationship has been PT may detect the presence of an inhibitor. The mixing established. study will be prolonged in the presence of an inhibitor. Fibrinogen, Fibrin, and Factor XIII Inhibitors Inhibitors are more time and temperature their specific clotting factors. To quantitate the levels of

stable than

Inhibitors of ? brinogen, ? brin, and factor XIII have been inhibitors, used

the

Bethesda

assay

is

most

reported. These inhibitors have occurred following plasma

commonly

in the United States. One Bethesda unit is defined as the transfusions or appeared spontaneously. Some patients have amount of antibody that will neutralize 50% of the inhiba common denominator of taking isoniazid, an antitubercuitor activity in a mixture of equal parts of normal plasma losis drug. and antibody containing plasma that has been incubated Factor II, VII, IX, and X Inhibitors for 2 hours at 37¡ãC. Detection of antiphospholipid antibody is based on proFactor II, VII, IX, and X inhibitors are rare. The causes for longation

of

phospholipid-dependent coagulation

assays.

factor inhibitor development are varied and include congenAntiphospholipid antibody is considered one of the most ciencies, immune disorders, and amyloidosis. common causes of a prolonged aPTT. Assays include the RusFactor XI and XII Inhibitors sell¡¯s viper venom time, kaolin clotting time, platelet neutralization procedure, and tissue thromboplastin inhibition test. Inhibitors

of

factors XI

and

XII

have

been

reported

other

hemostat

infrequently in patients with SLE, Waldenstr?m macroglobulinemia, and other disorders, as well as with chlorpromazImpaired Fibrinolysis ine administration. Impaired ? Clinical Presentation genetic and acquired in their origin. Impairment of ? brinolysis may predispose an individual to thrombosis. Patients The LA is the most commonly acquired and has an interwith type II hyperlipoproteinemia caused by familial hyperesting presentation. ic

In

the

absence

of

cholesterolemia demonstrate impairment of ? abnormalities, the LA is rarely associated with bleeding tenhigh incidence of recurrent thrombosis has been noted in dencies, even with surgical procedures. Bleeding episodes patients with hereditary de? ciencies of protein C or AT-III. in these patients are usually the result of thrombocytopenia Protein S de? ciency also joins the group of other plasma or another anomaly. Paradoxically, patients with LA are at protein de? increased risk for arterial and venous thromboembolism. (Table 24.19). De? Venous thrombosis

involving

the

leg

veins, with

associ-

have also been correlated with recurrent thrombosis. ated pulmonary emboli, is the most frequent complication. Spontaneous abortion and intrauterine deaths are Protein C De? increased in patients with LA. Protein C activity has been demonstrated to be related to the The presence of a speci? c factor inhibitor can be suscommonly occurring thrombotic episodes in patients with pected in patients with no history of bleeding episodes who and protein S. experience hemorrhage from various sites or in hemophiliac in patients with proteinuria patients not responsive to their usual dosage of blood proddecreased levels of protein C. Elevated prouct infusion. Bleeding episodes in hemophiliac patients with mechanism to inhibitors do not appear to be any more frequent or severe because

also

than in patients without inhibitors. When hemorrhagic events the anticoagulant activities of AT-III and protein C are probdo occur, treatment of a patient with inhibitor is dif? cult. ably complementary. CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

De? cient Patients With Recurrent Protein All Patients Thrombosis Protein C 12%¨C18% Protein S 15%¨C18% De? ciencies of protein C and protein S can be acquired anticoagulation characterized by resistance to APC is highly or

congenital. Acquired

de? ciencies

occur

in

DIC,

severe

prevalent in patients with venous thrombosis. This defect liver disease, vitamin K de? ciency, and oral anticoagulation appears to be at least 10 times more common in such patients therapy. Congenital de? ciencies are transmitted in an autothan any of the other known inherited de? ciencies of antisomal dominant fashion. Thrombotic complications usually coagulant proteins. The anticoagulant cofactor that corrects involve the venous system, although more recently protein S inherited APC resistance is identical to unactivated factor has been associated with arterial thrombosis as well. V. APC-resistant Several types

plasma contains of

protein

normal levels of C

defects have

procoagulant, which suggests that APC resistance may be

been

reported

ciency is characterized by caused by a selective defect in an anticoagulant function of low antigenic and functional levels of the protein. In those factor V (Fig. 24.2). ciency, the antigenic level of protein C is normal, but the function of the molecule is impaired. Two subtypes of the type II defect have been described: classic type IIa, Thrombin in which both chromogenic and clotting functional assays are abnormal, and type IIb, in which only the clotting functional method is abnormal. Protein C de? ciencies should, accordFactor VIII ingly, be screened by using a protein C functional assay (clot based or chromogenic), because this will detect both types I and II. Once a low level of protein C activity is determined, an immunological assay should be performed to distinguish type I from type II protein C de? ciency. Activated Protein C Resistance APC resistance, a new discovery, has been added to the list of may

causes of be

thrombotic

disease.

APC

resistance

ciency of an anticoagulant factor that functions as a cofactor to APC. APC resistance appears to be inherited as an autosomal dominant trait, suggesting C4b-binding protein that a single gene is involved. It is possible that patients with severe APC resistance are homozygous for the genetic defect, whereas an APC response closer to the normal range indicates heterozygosity. The genetically determined defect in Thrombin FIGURE 24.2. The protein C anticoagulant pathway. Thrombin converts factor VIII and factor V to their activated forms, factor

VIIIa and factor Va. A complex of thrombin with the endothelial cell receptor thrombomodulin activates protein C. APC inactivates factor VIIIa and factor Va on the platelet surface, and this reaction is accelerated by APC cofactor and free protein S. (Adapted with permission from Bauer KA. Hypercoagulability¡ªA new cofactor in the protein C anticoagulant pathway, N Engl J Med, 330(8):566, 1994. Copyright 1994 Massachusetts Medical Society. All rights reserved.) PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

Protein S De? in infancy. Familial studies indicate that patients with a de? protein S have an increased incidence of thrombosis. Early descriptions indicate that protein S de? common than either protein C or AT-III de? The congenital de? ciency of protein S is associated with an increased risk of recurrent juvenile venous and arterial thromboembolism. The association of a thrombotic diathesis with acquired protein S de? incidence of thrombosis because pregnancy, delivery, and oral contraceptives are causative factors. Defects of a qualitative nature (type II de? characterized by decreased heparin cofactor activity. This functional manifestation of defective AT-III is not associated with a reduction in molecular concentration. More than half of patients with type II de? ciency develop venous thrombosis. Congenital Protein S De? Decreased AT-III Levels: Congenital Diagnosis of protein S de?ciency differs signi? that of vitamin K¨Cdependent plasma proteins owing to protein S binding with C4b-BP and repartitioning between free (functional) and bound (nonfunctional) forms. The cation of congenital protein S is based on the comparison of functional and antigenic (free and total) as well as C4b-BP levels (Table 24.21). Currently, three types of congenital de? ciencies have been identi? ed: type I, low functional and antigenic protein S levels; type II, low functional protein S levels with a normal antigenic repartition (molecule dysfunctional); and type III, low functional protein S levels corresponding to a decrease in free antiThe

relative

incidence

of

congenital

AT-III de? cien

cy is between 1:2,000 and 1:5,000. AT-III de? ciency is inherited as an autosomal dominant disorder. Homozygotes have not been reported in AT-III de? ciency. Patients manifest signs and symptoms of between 10 and 30 years of age, their ? rst thrombotic event. An initial event is spontaneous in approximately half of patients. Women frequently experience manifestations during pregnancy or because of oral contraceptive use. Decreased levels of AT-III usually correlate the severity of venous thrombosis. Arterial thrombosis is a less common ?

with

genic protein S along with a normal decrease in free/functional protein S caused by increased synthesis of C4b-BP can occur transiently during acutephase reactions. A protein S functional assay should be used to screen for Decreased AT-III Levels: Acquired Acquired AT-III de? ciency can be caused by decreased synthesis, increased consumption, or other disorders; it can also be drug induced. The associated disorders are all types of protein S de? ciencies. Antigenic levels of both free and total forms of protein, as well as C4b-BP, will then be determined to differentiate types I, II, and III. Decreased synthesis: arteriosclerosis, cardiovascular disease, chronic hepatitis, cirrhosis, type II diabetes mellitus Increased consumption: DIC, homocystinuria, nephsyndrome,

postoperative, postpartum,

protein-losing

Antithrombin III De? enteropathy, pulmonary embolism, stroke, thrombophlebitis Drug induced: ? brinolysin, heparin, L-asparaginase, oral Hereditary defects of AT-III may tive or qualitative defects. Quantitative de?

be

caused by

quantita

contraceptives Other disorders: burns, malignancies is transmitted as an autosomal dominant disorder. Type I (quantitative) de? ciencies represent the majority of cases. Heparin Cofactor De? Familial studies reveal that severe thromboembolic probAlthough

deficiency

of

AT-III is

the

most

lems usually begin to be manifested in late adolescence or recurrent

thrombotic

complications

early adulthood. Manifestations of AT-III de?

have

been

associ-

common,

ated with a deficiency of heparin cofactor II. The latter CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

defect is manner.

inherited

in

an

autosomal

dominant

Patients with venous thromboembolism can be divided Sympathetic heterozygous patients exhibit about half the groups. The ? normal plasma levels of heparin cofactor II activity. This as cancer, as recent deficiency results from defective protein synthesis rather or an acquired abnormality as the LA that is than from a qualitative abnormality. Heparin cofactor II known to increase the risk of thrombosis. The pathophysioldeficiency can also be demonstrated in patients with DIC. is poorly understood (Table 24.22). In these situations, both AT-III and heparin cofactor II consists of patients without the usual levels are diminished in parallel. risk factors that predispose people to venous thrombosis. In some of these patients, it is possible to identify a de? ciency Clinical Signs and Symptoms of AT-III, protein C, or protein S, and family studies show Clinical presentations of patients with de? ciencies of naturally occurring anticoagulants are similar. De? 50% of normal for protein C, protein S, and AT-III may lead to serious thrombotic events. Frequent presenting conditions include thrombophlebitis, deep venous thrombosis, pulmonary emboli. The frequency of protein de? cienhereditary defects. APC resistance occurs in about one third of patients. Precipitating factors for thrombosis, as pregnancy and the use of oral contraceptives, are identi? ed

such

in 60% of these patients. APC resistance appears to be 5 to 10 times more common than a de? ciency of AT-III, protein C, or protein S in patients with venous thrombosis. cies correlated with recurrent thromboembolic disease is as Protein S: 5% to 10% Protein C: 7% Laboratory Assessment of HypercoagulableStates AT-III: 2% to 4% Four major areas of clinical testing are available to evaluate a patient for hypercoagulability. These categories are Venous Thromboembolism 1. Natural anticoagulants¡ªprotein C de? ciency, protein S Venous thromboembolism has

an

incidence

of

300,000

de? ciency, factor V (Leiden), antithrombin de? ciency, episodes per year in the United States, and the complication and heparin cofactor II de? of pulmonary embolism causes 5% to 10% of all deaths in Fibrinolysis¡ªplasminogen ciency, poor tissue plasmithe hospital. Venous thrombosis can result from hereditary nogen activator release, excessive plasminogen activator or acquired factors or both. inhibitor, and dys? PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

3. Antiphospholipid antibodies¡ªACAs, LA Another disorder related to ineffective thrombopoiesis is 4.

Hyperhomocysteinemia

ciency anemia, which usually results in a decrease in megakaryocyte size and the suppression of megakaryocyte endoproliferation and size. Hereditary thrombocytopenias CHAPTER HIGHLIGHTS

include Fanconi syndrome, constitutional aplastic anemia and its variants, amegakaryocytic thrombocytopenia (TAR Vascular Disorders thrombocytopenia, Wiskott-Aldrich syndrome,

May-Hegglin

anomaly,

Abnormal bleeding involving the loss of red blood cells from and

hereditary

macrothrombocytopenia

(e.g., Alport

the microcirculation expresses itself as purpura, which is characterized by hemorrhages into the skin, mucous membranes, and internal organs. Purpura may be associated with a variety of vascular abnormalities including direct endothelial cell damage, an inherited disease of the connective tissue, decreased mechanical strength of the microcirculation, mechanical disruption small venules, microthrombi (small clots), and vascular malignancy.

of

Increased destruction or utilization of platelets may result from a number of mechanisms. It can be caused by antigens, antibodies, drugs, or foreign substances. Bacterial sepsis causes increased destruction of platelets owing to the attachment of platelets to bacterial antigen-antibody immune complexes. Antibodies of either autoimmune or isoimmune origin may produce increased destruction of platelets. Accelerated consumption of platelets is another cause Abnormal Platelet Morphology of thrombocytopenia. One of the most important and frequently encountered forms of increased of When examining a peripheral blood smear for platelets, the morphology of the platelets should be observed. Abnormal variations in size should be noted. Disorders of platelet size include Wiskott-Aldrich syndrome, May-Hegglin anomaly, Alport syndrome, and Bernard-Soulier syndrome. platelets is ITP. This antibody-related response, which may be preceded by infection, is believed to have a devastating effect on platelet survival. ITP may complicate other antibody-associated disorders such as SLE. Patients with ITP usually demonstrate petechiae, bruising, menorrhagia, and bleeding after minor trauma. Quantitative Platelet Disorders Disorders of Platelet Distribution The normal range of circulating platelets is 150 ¡Á 10 /L to A platelet distribution disorder can result from a pooling

consumption

450 ¡Á 10 /L. When the quantity of platelets decreases to levels of platelets in the spleen, which is frequent if splenomegaly below this range, a condition of thrombocytopenia exists. If the is present. This type of thrombocytopenia develops when quantity of platelets increases, thrombocytosis is the result. more than a double or triple increase in platelet production Thrombocytopenia

can

result from

a

wide

variety of

is required to maintain the normal quantity of circulating conditions, poreal

such

as

following

the

use

of

extracor

platelets. circulation in cardiac bypass surgery or in alcoholic liver ned as a substantial increase disease. ly

HIT

and

associated

thrombotic

events, relative

in circulating platelets over the normal upper limit of 450 ¡Á common side effects of heparin therapy, can cause substan10 /L. Thrombocytosis is usually grouped according to cause: tial morbidity and mortality. Most thrombocytopenic condireactive or benign etiologies versus platelet elevations linked ed into the major categories of disorders c hematological disorder. of production, disorders of destruction, and disorders of platelet distribution and dilution. Decreased production of platelets may be caused by hypoQualitative Platelet Disorders proliferation of the megakaryocytic cell line or ineffective If platelets function

are

normal in

number but

fail

thrombopoiesis caused by acquired conditions or hereditary properly, one of four separate categories of platelet dysfunction

can

exist. These

include the

more

common

to

Thrombocytopenia

caused by

hypoproliferation

can

acquired and less frequent hereditary causes. Hyperactive result from acquired damage to hematopoietic cells of the platelets associated with hypercoagulability and thrombobone marrow caused by factors such as irradiation, drugs sis make up an additional category of abnormal platelet and cancer chemotherapeutic agents, chemicals, and alcohol. function. Hypoproliferation may also result from nonmalignant conAcquired platelet function defects can be caused by a ditions,

such

as

infections,

lupus

erythematosus, granu-

blood plasma inhibitory substance. In addition, acquired lomatous disease such as sarcoidosis, and idiopathic causes. platelet dysfunction is commonly seen in the myeloproIneffective thrombopoiesis may result in decreased platelet liferative

syndromes

and

production. the

Thrombocytopenias

uremia. Miscellaneous

disor-

of

may

this

type

be

ders can be associated with platelet dysfunction. Many manifestation of a nutritional disorder, such as a de? drugs can induce platelet function defects, resulting in of vitamin B

or folic acid.

hemorrhage. CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

Hereditary disorders include adhesion and pelvic surgery, shock, advanced malignancy, septicemia, Bernard-Soulier syndrome; primary aggregation disorders, and intravascular hemolysis. such as Glanzmann thrombasthenia and essential athromand

secondary

recognized

disorder;

bia; and secondary aggregation disorders, such as hereditary extreme

complications

intravascular

and

of

storage pool defect and hereditary aspirin-like defects. extravascular

disorders

and

life-threatening consequences. brinolysis

is

associated

with

Bleeding Disorders Related to Blood Clotting conditions ytic mechanism

in

which

gross

with

subsequent

activation

of

the

? brinogen

and

coagulation

Bleeding and defective ? brin clot formation are frequently related to a coagulation factor. Disorders of the blood coagulation factors can be grouped into three categories: defective production, excessive destruction, and inhibition. A condition of defective production may be related to a de? ciency of vitamin K. Severe liver disease may produce brinogen, although low levels of ? brinogen rarely produce hemorrhage. Hereditary clotting defects including classic hemophilia (hemophilia A) and von Willebrand disease are examples of hereditary disorders that represent functionally inactive factor VIII. understanding the molecular pathological processes that underlie hereditary factor consumption occurs. The important characteristic of primary ? brinolysis is that no evidence of ? brin deposition occurs. Primary ? brinolysis occurs when large amounts of plasminogen activator enter the circulatory system as a result surgery, or malignancies. Although the same clinical conditions may also induce secbrinolysis or DIC, the distinction between the two is essentially in the demonstration of ? brin formation. In secbrinolysis, excessive clotting and ? brinolytic activity monomers are detectable because of the action of thrombin on the ? brinogen molecule. This ? brinolytic process is only caused by excessive clotting; therefore, it is a secondary condition. This distinguishes between primary and secondary ? brinolysis. disease. The cloning of factor VIII facilitated the identi? of mutations that lead to hemophilia A, an inherited de? ciency The Hypercoagulable State of factor VIII coagulant activity that causes severe hemorrhage. von Willebrand disease may be an acquired or inherited

? brinol

pathological

disorder. The congenital disorder is autosomally dominant in most cases. Three broad types of von Willebrand disease are recognized. In addition, a platelet-type von Willebrand disease (pseudo¨Cvon Willebrand disease) is caused by an abnormal platelet receptor for vWF. Acquired von Willebrand disease may complicate other diseases such as lymphoproliferative and autoimmune disorders, and proteolytic degradation of vWF complicates myeloproliferative disorders. A de? ciency of factor IX is known as hemophilia B or Christmas disease. A de? ciency of factor XI is referred to as hemophilia C. Fibrinogen de? ciency as a genetic disorder may represent a defect of production or dysfunctional molecules. Hereditary de? ciencies of the other coagulation factors are relatively rare. Examples of rare defects include ciency, in which no clinical bleeding tendencies are apparent, and factor XIII de? ciency, which is associated with spontaneous abortion and poor wound healing. Thrombi may form because coagulation is enhanced or because protective devices such as ? brinolysis are impaired. An increase in the likelihood of blood to clot is referred to as the hypercoagulable state. Hypercoagulable states include various inherited and acquired clinical disorders characterized by an increased risk for thromboembolism. Primary hypercoagulable states include relatively rare inherited conditions that lead to disordered endothelial cell thromboregulation. These conditions include decreased thrombomodulin-dependent activation of APC, impaired heparin binding of AT-III, or downregulation of membrane-associated plasmin generation. The major inherited inhibitor disease states include ATciency, and protein S de? Secondary hypercoagulation states may be seen in many heterogeneous disorders. Acquired inhibitors of clotting proteins, also known as circulating anticoagulants, inactivate or inhibit the usual procoagulant activity of coagulation factors. Inhibitors are frequently characterized as speci? c, those directed against Disorders of Destruction and Consumption a coagulation factor, or nonspeci? c, those directed against a complex of factors, such as the LA. The majority of these Blood by

coagulation

factors can

be

destroyed

in

vivo

inhibitors exhibit biochemical properties, suggesting they are enzymatic of

degradation

or

by

pathological

immunoglobulins. Inhibitors may arise following transfusion coagulation with excessive utilization of the clotting factors. of blood products or in patients with no previous hemostatic

activation

Enzymatic destruction can result from bites by certain species disorders. Acquired inhibitors can be a signi? cant cause of of snakes whose venom contains an enzyme that degrades hemorrhage. brin monomer. In vivo activation Speci? c IX,

inhibitors

against factors II,

V,

VII,

VIII,

of coagulation by tissue thromboplastin¨Clike materials can XII, and XIII and vWF have been detected in patients with Conditions individual factor de? ciencies. However, some inhibitors of that

can

cause

this

consumption

of

coagulation

VII, IX, and XII and vWF have been observed in include obstetrical complications, trauma, burns, prostatic ciencies of coagulation factors. PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

In this case, an increased aPTT with a that the patient is de? VIII, IX, XI, or XII. Factor substitution testing might be valuable before a factor assay is performed. This screening test is useful in isolating either speci? tors that are de? factor de? ciency, a formed. In this case, a cient in factor VIII. physician was concondition. He did not rememnormal, 10 to 15 seconds), and the aPTT was 55 seconds (continued)

factors

CHAPTER 24

¡ö

Disorders of Hemostasis and Thrombosis

prolonged aPTT. Either a would be more common. 2.

Factor substitution studies would be valuable. If the sub-

stitution studies reveal an abnormality, a assay should be conducted. 3.

In this case, factor VIII activity was found to be decreased

(patient, 30% activity; and the lack of a not have Further testing was performed. The results were lows:

bleeding

time

increased,

platelet

aggregation

decreased, factor VIII decreased, and factor VIII/vWF decreased. Based on these ? sic hemophilia was excluded. The laboratory diagnosis of von Willebrand disease. The laboratory ? as follows: (continued) PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

the outpatient laboratory for a hematocrit, and coagulation pro? Hemoglobin 10.0 g/L Hematocrit 27% coagulation pro? Bleeding time 7 minutes (normal, 1 to 3 minutes) PT 11 seconds (control, 12.2 seconds) aPTT 29 seconds (control, 34 seconds) Clot retraction decreased

1. What additional tests would be suggested based on the initial laboratory results? 2. What would the Wright-stained blood ? 3. What is the most likely diagnosis and prognosis? A platelet count and qualitative platelet studies would be appropriate follow-up procedures in view of the prolonged bleeding time and poor clot retraction. platelet disorder is suspected, the peripheral blood be valuable. Obviously, would support in platelet size distribution and morphology 3.

Further testing for platelet function revealed a de?

in both platelet aggregation and adhesion. The diagnosis of Glanzmann thrombasthenia was made. This autosomal recessive disorder usually becomes less severe as patient ages. In this woman¡¯s case, severe bleeding or future surgical interventions would need to be supported by the use of platelet concentrates. _____ Bernard-Soulier syndrome secondary

fibrinolysis

is

Giant platelets presence of B.

Smallest platelets seen

brin split products C.

Large platelets

brin degradation products ? brin monomers Questions 5 through 7: Match the etiologies of these plate-

all of the above let dysfunctions with the appropriate associated disorder (use an answer only once). _____ Acquired _____ Drug induced _____ Hereditary DIC is characterized by microvascular thrombosis ? brin deposition brinolysis all of the above von Willebrand disease Which of the following factors can contribute to hypercoagulation? Which of the following parameters can be abnormal in classic von Willebrand disease type I? Bleeding time Vascular endothelial damage Increased blood ? Decreased platelets Decreased titers of clotting factors Platelet count Questions 15 through 19: Match the following. All of the above _____ Antithrombin III de? The most common form of von Willebrand disease is _____ Oral contraceptives _____ Protein C de? _____ Cancer _____ Pregnancy all have about the same incidence Primary hypercoagulable state Laboratory results in acute DIC re? Secondary hypercoagulable state in which of the following coagulation components? Platelet function Excessive clotting and ? Accelerated thrombin formation Fibrin formation Primary ?

gross activation of the ? consumption of ? consumption of coagulation factors all of the above Questions 20 through 22: Match the following terms with the appropriate description. _____ Circulating anticoagulants _____ LA _____ Factor VIII inhibitor factor inhibitor Acquired inhibitors of clotting proteins Also known as antiphospholipid or anticardiolipin BIBLIOGRAPHY Bromberg

ME.

Immune thrombocytopenic

purpura-the

changing

therapeutic landscape, N Engl Med, 355(16):1643¨C1645, 2006. Adcock DM. Is there a genetic relationship between arterial and venous eld P, Perotta PL. Recognizing HIT, Adv Lab, 16(2):42¨C43, 2007. thrombosis? Clin Lab Sci, 20(4):221¨C223, 2007. Castellone D. A case study in coagulation, Adv Lab, 15(1):51¨C53, Agapitov AV, Haynes WG. Role of endothelin in cardiovascular disease, J Renin Angiotens Aldost Syst, 3(1):1¨C15, 2002. Cazzola M. ogica,

Molecular

basis

of

thrombocytosis,

Arepally GM, Ortel TL. Heprin-induced thrombocytopenia, N Engl 93(5):646¨C648, 2008. Med, 355(8):809¨C817, 2006. Dahlb?ck B. Advances in understanding pathogenic mechanisms of Aster RH, Bougie DW. Drug induced immune thrombocytopenia, N thrombophilic disorders, Blood, 112(1):19¨C27, 2008. Engl Med, 357(6):580¨C587, 2007. Danese S, et al. The protein C pathway in tissue in? Bates SM, Ginsberg JS. Treatment of deep-vein thrombosis, N Engl injury: pathogenic role and therapeutic implications, Blood, 115(6), Med, 351(3):268¨C277, 2004. 1121¨C1130, 2010.

Haematol

Bernard GR, et al. Ef? Drygalski AV, et al. Vancomycin-induced immune thrombocytopenia, protein C for severe sepsis, N Engl J Med, 344(10):699¨C709, 2001. N Engl Med, 356(9):904¨C910, 2007. PART 5 ¡ö

Principles and Disorders of Hemostasis and Thrombosis

Federici AB. VWD, Blood,

VWF

propeptide:

a

useful marker in

Passamonti F, et al. Prognostic factors for thrombosis, myelo? 108(10):3229, 2006. and leukemia in essential thrombocythemia: a study of 605 patients, Fritsma Clin Lab

GA. Sci,

Managing 16(2):

the

bleeding

patient,

Haematologica, 93(11):1645¨C1651, 2008. 107¨C110, 2003. Patrono C. Aspirin as an antiplatelet drug, N Engl J Med, 330(18): Fritsma GA, Marques MB. Top 10 problems in coagulation, Adv Med 1287¨C1294, 1994. Lab Prof, 16(13):22¨C29, 2004. Peter K. Proteomics Blood, 115(20):

unravels

platelet

function,

Fritsma MG. Use of blood products and factor concentrates for coagu4008¨C4009, 2010. lation therapy, Clin Lab Sci, 16(2):115¨C119, 2003. Provan D, et al. International consensus report on the investigation Gardner J. Factor V Leiden with deep venous thrombosis, Clin Lab Sci, and management of primary immune thrombocytopenia, Blood, 16(1):6¨C9, 2003. 115(2), 168¨C186, 2010. George JN, purpura,

et

al.

Chronic idiopathic

thrombocytopenic

Rivera-Begeman A, et al. New-onset thrombocytopenia and anemia N Engl J Med, 331(18):1207¨C1215, 1994.

in a patient with a complex medical history, Labmedicine, 37(1): Giannakopoulos B, et al. Current comcepts on the pathogenesis of the 24¨C27, 2006. antiphospholipid syndrome, Blood, 190(2):422¨C430, 2007. Refaai MA, Laposata M. A primer on bleeding and thrombotic disorGiannakopoulos B, et al. How we diagnose the antipholipid syndrome, ders, Adv Admin Lab 12(4):46¨C55, 2003. Blood, 113(5):985¨C994, 2009. Refaai MA, Laposata M. Heparin-induced thrombocytopenia, Clin Grody g

WW, Telatar M. factor

Multiplex

SNP

analysis:

Lab News, 29(10):10¨C12, 2003. V R506Q (Leiden) mutations, Am Biotechnol Lab, 21(2):34¨C38, 2003. Ridker PM, et al. Ethnic distribution of Factor V Leiden in 4047 men Haberichter SL, et al. Assay of the von Willebrand factor (VWF) Med, 277(16):1305¨C1307, 1997. propeptide to identify patients with type 1 von Willebrand disease Ridker PM, et al. Long-term, low-intensity warfarin therapy for the with decreased VWF survival, Blood, 108(10):3344¨C3351, 2006. prevention of recurrent venous thromboembolism, N Engl J Hajjar KA.

Factor V

Leiden¡ªAn

unsel?

348(15):1425¨C1434, 2003. 330(23):1585¨C1586, 1994. Sadler JE. Von Willebrand factor, ADAMTS13, and thrombotic thromIngram GIC. The history of haemophilia, J Clin Pathol, 29(6):469¨C479, bocytopenic purpura, Blood, 112(1):11¨C18, 2008. Schneider M. Thrombotic microangiopathy (TTP and HUS): advance Kakkar N, Gupta V. Spurious thrombocytopenia in a young male, 20(4):216¨C220, Labmedicine, 39(8):463¨C464, 2008.

Screenin

Kashyap AS, et al. Treatment of von Willebrand¡¯s disease, N Engl Svensson PJ, Dahlback V. Resistance to activated protein C as a J Med, 351(22):2345, 2004. Med, 330(8):517¨C522, 1994. Kasirer-Friede A, et al. Role of ADAP in shear ? ow-induced platelt Taylor LJ. Laboratory management of the bleeding patient, Clin Lab mechanotransduction, Blood, 115(11), 2274¨C2282, 2010. 16(2):111¨C114, 2003. Kurtz ME. Diagnostic dilemmas of mild bleeding disorders, Adv Lab, Thrasher

AJ.

Wiskott-Aldrich 9(9):38¨C42, 2000. Soc

Hematol,

Education

Book,

132¨C136,

Lambert MP. Childhood ITP:knowing when to worry? Blood, 114(23) 4758¨C4759, 2009. Triplett DA. Laboratory diagnosis of von Willebrand¡¯s disease, Mayo Laposata M. Whom to monitor for hypercoagulability¡ªReport of the Clin Proc, 66:832¨C840, 1991. CAP Consensus Conference on Thrombophilia Testing. Presented Triplett DA. Coagulation and bleeding disorders: review and update, June 27, 2003, Cambridge, MA, Curr Concept Clin Pathol. 46(8B):1260¨C1269, 2000. Lange RA, Hillis, LD. Concurrent antiplatelet and ? Van Cott EM. Heparin-induced thrombocytopenia and its manageN Engl J Med, 352(12):1248¨C1250, 2005. ment with new anticoagulants. Presented June 27, 2003, Mannucci PM. Treatment of von Willebrand¡¯s diease, N Engl J Med, MA, Curr Concept Clin Pathol. 351(7):683¨C694, 2004. Wagner DD, Bonfanti R. von Willebrand factor and the endothelium,

Marques MB. Treatment of single factor de? ciencies: A case study Mayo Clin Proc, 66:621¨C627, 1991. approach, Clin Lab Sci, 16(2):120¨C122, 2003. Warkentin TE. Drug-induced immune-mediated thrombocytopenia Martin VL, et al. D-dimer: more than just a number, Part 1, Adv Lab, from purpura to thrombosis, N Engl J 356(9):891¨C893, 2007. 15(1):68, 2006. Williams JL. Introduction: new directions in hemostasis and coagulaMonahan PE, White GC. Hemophilia gene therapy: Update, Curr 20(4):215, 2007. Opin Hematol, 9(5):430¨C436, 2002. Williams JL. Cross talk between the in? ammation and coagulation Moroose R, Hoyer LW. von Willebrand factor and platelet function, 20(4):224¨C229, 2007. Annu Rev Med, 37:157¨C163, 1986. Yarranton H, Machin SJ. Thrombotic thrombocytopenic purpura: Nachman RL, Silverstein R. Hypercoagulable states, Ann Intern Med, New approaches to diagnosis and management, Blood Ther Med, 119(8):819¨C827, 1993. 2(3):82¨C91, 2003.