Bleeding Time & Clotting Time

BLEEDING TIME CLOTTING TIME Bleeding time Bleeding time is a medical test done on someone to assess their platelet function. It is a blood test that looks at how fast small blood vessels in the skin close to stop you from bleeding.

Process: It involves cutting the underside of the subject's forearm, in an area where there is no hair or visible veins. The cut is of a standardized width and depth, and is done quickly by an automatic device. A blood pressure cuff is used above the wound, to maintain venous pressure at a special value. The time it takes for bleeding to stop (i.e. the time it takes for a platelet plug to form) is measured. Cessation of bleeding can be determined by blotting away the blood every several seconds until the site looks 'glassy'.

Bleeding time is used to measure the duration of bleeding after a measured skin incision. Bleeding time may be measured by one of three methods: template, Ivy, or Duke. The template method is the most commonly used and the most accurate because the incision size is standardized. Bleeding time depends on the elasticity of the blood vessel wall and on the number and functional capacity of platelets. Although this test is usually performed on patients with a personal or family history of bleeding disorders, it's also useful- along with a platelet count for preoperative screening. The test is usually not recommended for patients with a platelet count of less than 75,000/u1.

Purpose • To assess overall hemostatic function (platelet response to injury and functional capacity of vasoconstriction). • To detect congenital and acquired platelet function disorders. Patient preparation • Explain to the patient this test is used to measure the time required to form a clot and stop bleeding. • Tell him who will perform the test and when it will take place. • Inform him that he need not restrict food or fluids before the test. • Reassure the patient that, although he may feel some discomfort from the incisions, the antiseptic, and the tightness of the blood pressure cuff, the test takes only 10 to 20 minutes to perform. • Advise the patient that the incisions will leave two small, hairline scars that should be barely visible when healed.

• Check the patient's history for recent use of drugs that prolong bleeding time, including sulfonamides, thiazide diuretics, antineoplastics, anticoagulants, non steroidal anti-inflammatory drugs, aspirin and aspirin compounds, and some non narcotic analgesics. If the patient has taken such drugs, check with the laboratory for special instructions. If the test is being used to identify a suspected bleeding disorder, it should be postponed and the drugs discontinued. If the test is being used preoperatively to assess hemostatic function, it should proceed as scheduled.

Equipment Blood pressure cuff, disposable lancet, template with 9-mm slits (template method), 70% alcohol or povidone-iodine solution, filter paper, small pressure bandage, stopwatch. Procedure and posttest care 1- Template method: Wrap the pressure cuff around the upper arm and inflate the cuff to 40 mm Hg. Select an area on the forearm with no superficial veins, and clean it with antiseptic. Allow the skin to dry completely before making the incision. Apply the

appropriate template lengthwise to the forearm. Use the lancet to make two incisions, I mm deep and 9 mm long. Start the stopwatch. Without touching the cuts, gently blot the drops of blood with filter paper every 30 seconds, until the bleeding stops in both cuts. Average the time of the two cuts, and record the result.

2- Ivy method: After applying the pressure cuff and preparing the test site, make three small punctures with a disposable lancet. Start the stopwatch immediately. Taking care not to touch the punctures, blot each site with filter paper every 30 seconds, until the bleeding stops. Average the bleeding time of the three punctures, and record the result.

3- Duke method: Drape the patient's shoulder with a towel. Clean the ear-lobe, and let the skin air-dry. Then make a puncture wound 2 to 4 mm deep on the earlobe with a disposable lancet. Start the stopwatch. Being careful not to touch the ear, blot the site with filter paper every 30 seconds, until bleeding stops. Record bleeding time. • In a patient with a bleeding tendency (hemophilia, for example), maintain a pressure bandage over the incision for 24 to 48 hours to prevent further bleeding; check the test area frequently; keep the edges of the cuts aligned to minimize scarring. • In other patients, a piece of gauze held in place by an adhesive bandage is sufficient. •

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Precautions • Be sure to maintain a cuff pressure of 40 mm Hg throughout the test. • If the bleeding does not diminish after 15 minutes, discontinue the test.

Reference

values

The normal range of bleeding time is from 3 to 6 minutes in the template method; from

3 to 6 minutes in the Ivy method; and from I to 3 minutes in the Duke method

Abnormal findings

Prolonged bleeding time may indicate the presence of disorders associated with thrombocytopenia, such as Hodgkin's disease, acute leukemia, disseminated intra vascular coagulation, hemolytic disease of the newborn.

Interfering factors • Sulfonamides, thiazide diuretics, antineoplastics, anticoagulants, nonsteroidal antiinflammatory drugs, aspirin and aspirin compounds, and some nonnarcotic analgesics (prolonged bleeding time).

CLOTTING TIME Clotting time: the time required for a sample of blood to coagulate in vitro under standard conditions is called "clotting time". Clotting is the formation of a jelly like substance over the valves of the blood vessels resulting in stoppage of blood flow. Clotting is a natural defense mechanism to prevent blood loss from the body. A clot is usually formed within 5 minutes after injury. Whenever a blood vessel is cut there is a rush of platelets causes a cut or injury to be filled and thus bleeding stops. Clotting is initiated by two pathways i.e intrinsic pathway and extrinsic pathway. There are various methods for determining the clotting time, the most common being the capillary tube method. It is affected by calcium ion levels and many diseases. Normal value of clotting time is 5-8 minutes. Other methods for measuring clotting time are slide method

"WHOLE BLOOD COAGULATION (CLOTTING) TIME (LEE-WHITE)" Principle: The whole blood clotting time is a rough measure of all intrinsic clotting factors in the absence of tissue factors. Variations are wide and the test sensitivity is limited. Whole blood, when removed from the vascular system and exposed to a foreign surface, will form a solid clot. Within limits, the time required for the formation of the solid clot is a measure of the coagulation system. Reagents and Materials: (1) Stop watch equipment for collection of blood. (2) 2 plastic syringes. (3) 3 clean, dry glass test tubes (10 x 75 mm). (4) Water/dry bath (at 37oC).

Procedure: (1) Label glass tubes #1, #2, and #3. (2) Collect at least 2 ml of blood in a plastic syringe. Discard this blood.(This prevents tissue thromboplastin from entering the blood sample.) Change syringes. (3) Collect at least 5 ml of blood in the second plastic syringe. (4) Approximately 1 ml of blood is placed in each of the three glass test tubes. (#3 first, then #2, then #1) (5) The stopwatch is started as soon as the blood enters the first tube #3. (6) All tubes are placed into the 37°C water bath. (7) Gently tilt tube #3 (45 angle) every 30 seconds, until the blood in it clots. (8) Thirty seconds after tube #3 clots, proceed with tube #2, tilting every 30seconds, until a clot is formed. (9) Thirty seconds after tube #2 is clotted, tube #1 is tilted until no flow ofblood is observed on tilting.

(10) Record the time. The coagulation time is the time required for the bloodto clot in the last tube. (Tube #1)

Ref Range: This range should be between 5 to 10 minutes. Range of Values.(1)Normal values: 5 to 15 minutes.(2)Critical value: Less Than Greater Than Not applicable 15 minutes Special notes.(a) The following variables tend to decrease the clotting time: rough handling of the blood specimen, presence of tissue fluids (traumatic venipuncture),frequent tilting of the tube, and unclean tubes.(b) The following variables tend to increase the clotting time: extreme increases in temperature, variation in pH, and performance of the test at room temperature.(c) This test is of value primarily as it was used to follow heparin therapy. Its use as a screening procedure is limited due to its poor sensitivity.(d) The whole blood clotting time is affected mainly by defects in the intrinsic pathway factors and by defects in fibrin and fibrinogen. It is not sensitive to platelet abnormalities.(e) A prolonged clotting time immediately indicates impairedcoagulation, but a normal clotting time does not exclude many serious clotting defects.(f) One disadvantage of the whole blood clotting time is its relative lack of reproducibility.(g) This procedure has been replaced in most laboratories with the APTT, which is more reproducible and easily controlled.(h) The coagulation time is normal in thrombocytopenic purpura. This is explained by the fact that only a small number of thrombocytes need be present for normal coagulation to take place. Lee-White is not recommended for evaluating heparin therapy - Lacks reproducibility