Chemistry Contents General ....................................................................................................................2 Instruments ..............................................................................................................3 Statistics and Quality control .................................................................................... 10 Diabetes Mellitus .................................................................................................... 14 Lipids ..................................................................................................................... 17 Proteins ................................................................................................................. 20 Kidney Functions ..................................................................................................... 22 Electrolytes and Minerals ......................................................................................... 28 Acid base and ABG .................................................................................................. 31 Liver ...................................................................................................................... 34 Enzymes................................................................................................................. 39 Biological fluids ....................................................................................................... 43 GIT ........................................................................................................................ 48 Hormones .............................................................................................................. 49 Panic Values ........................................................................................................... 53 Geriatrics ............................................................................................................... 53 Tumor markers ....................................................................................................... 54
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1
Chemistry
General Chemistry
General 1.
The source of NADPH is: a. EMP pathway. b. HMP shunt. c. Kreb’s cycle. d. Oxidative phosphorylation.
Probable answer: HMP shunt Hexose monophosphate shunt: Significance: - Production of NADPH from NADP (the major source of NADPH): NADPH is required: a. For biosynthetic reactions of fatty acid, cholesterol, drug reduction, b. As a cofactor for some non-synthetic enzymatic reactions. c. For production of ribose for nucleotide and nucleic acid synthesis. d. To allow the entry of some carbohydrates into the glycolytic pathway (especially ribose, but also some others), and therefore acts as a connection route between different pathways Embden–Meyerhof–Parnas (EMP pathway) and Glycolysis: - The metabolic pathway that converts glucose into pyruvate. The free energy released is used to form ATP and NADH. - The most common type of glycolysis is the EMP pathway. Kreb’s cycle (=Citric acid cycle) - A series of aerobic enzyme-catalyzed chemical reactions - starts with pyruvate, which is the end product of gylcolysis, - used to generate energy through the oxidation of acetate derived from carbohydrates, fats and proteins into CO2 and ATP. - Provides precursors of certain amino acids as well as the reducing agent NADH Oxidative phosphorylation: - The process in which ATP is formed as a result of the transfer of electrons from NADH to O 2 by a series of electron carriers. - The major source of ATP in aerobically e.g. generates 26 of the 30 molecules of ATP that are formed when glucose is completely oxidized to CO2 and H2O.
1.
Osmolarity= a. Grams solute /liter solution b. Moles solute /Kg solution c. Moles solute /Kg water d. Moles solute /liter water
Probable answer: moles solute /Kg of water Osmolality: moles of solute per L of solution (osmol/L) Osmolarity: moles of solute per Kg of solvent. (osmol/kg). Solution concentration = grams of solute per liter solution (g/L) Aqueous solution: If the solvent is water, then the solution is called an aqueous solution
2.
When glucose is converted to lactate or pyruvate this is called: a. Glucolysis. b. Gluconeogenesis c. Glycogenesis d. Glycogenolysis e. Glycolysis
Probable answer: Glycolysis. - Glycolysis is the conversion of glucose, into pyruvate with the production of ATP and NADH. - Glycogenesis is the process the process of glycogen synthesis. - Glycogenolysis is the breakdown of glycogen to glucose-1-phosphate and glycogen(n-1). - Gluconeogenesis is the generation of glucose from non-carbohydrate carbon substrates e.g. pyruvate, lactate, glycerol, glucogenic amino acids, and odd-chain fatty acids.
3.
Which analyte is mostly affected by hemolysis: a. AST. b. ALT c. Glucose d. Calcium
Probable answer: AST. Laboratory tests affected by hemolysis: Seriosly affected Notieably affected Potassium Serum Iron LDH ALT AST T4 CBC
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2
Slightly affected Phosphorus Total protein Albumin Mg, Ca Acid phosphatase
Chemistry
Instruments
Instruments 4. Lamp emits infrared radiation:
probable answer: Tungestin filament lamp IR region has WL > 650 nm, UV region has WL2% of the exciting light. This is caused by a loss of excitation intensity across the cuvet path length as the excitation light is absorbed by the fluorophore. Thus; ↑fluorophore concentration
↑ absorbance of the excitation intensity
↑ loss of the excitation light as it travels through the cuvette
This effect is most often encountered with a right angle fluorescence instrument, in which the emission slits are set to monitor the center of the sample cell where the absorbance of excitation light is greater than at the front surface of the cuvet. Elimination of the filter effect: - Front surface approach provides the greatest linearity over a broad range of concentration because it minimizes the inner filter effect.
However, it is more susceptible to background light scatter. - Most fluorescence measurements are made on very dilute solutions, and the inner filter effect is therefore not a problem.
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7
Chemistry
Instruments
20. Concentration is directly proportional to :
Probable answer: absorbance , log transmittance Beer's law states that the concentration of a substance is directly proportional to the amount of light absorbed or inversely proportional to the logarithm of the transmitted light. Mathematically, Beer's law is expressed as A = abc, where: A= Absorbance a= Proportionality constant defined as absorptivity b= Light path in centimeters c= Concentration of the absorbing compound, usually expressed in grams per liter.
21. Most accurate and rapid for immunoglobulins: a. Turbidimetry, b. Radioimmunoassay, c. Radioimmunodiffusion, d. Protein electrophoresis, e. Immunofixation
Probable answer: a. Turbidimetery. For evaluation of immunoglobulins qualitative and quantitative tests are available. Immunoglobulin molecules of a particular class or subclass are recognized by their constant region of the heavy (or light) chain. Specific antibody is recognized by the variable region directed to an antigenic epitope of the antigen. A. Qualitative Assessment (Electrophoretic Methodologies) 1. Zone electrophoresis: A qualitative (semiquantitative) technique that normally yields five bands: albumin, α1, α2, β, and γ-globulin fractions. Immunoglobulins normally fall in γ-globulin band, although they also migrate into β and α2 globulin bands. Useful for assessing total protein status and to screen for monoclonal immunoglobulins. 2. Immunoe1ectrophoresis (IEP): Used primarily for the characterization of monoclonal immunoglobulins. Now largely replaced by immunofixation electrophoresis. 3. Immunofixation electrophoresis (IFE): Easier to interpret and more sensitive than IEP. The test currently represents the standard clinical laboratory approach for identification of monoclonal or oligoclonal immunoglobulins. B. Quantitative Assessment (Precipitin Methodology) 1. Double gel diffusion: Lacks sensitivity of many quantitative methods, Technically easy, can be performed with antigen preparations that are only partially purified, is highly specific, and serves as a useful screening test for the presence of an antibody or antigen particularly in a heterogeneous sample. Currently is used infrequently in clinical laboratories.
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8
Chemistry
Instruments 2. Single radial immunodiffusion: Simple and reliable method. Used to quantify: - Immunoglobulins (including IgG subclasses), - complement components (e.g., C3, C4, and factor B), - other proteins. 3. Nephelometry: In contrast to precipitin reactions, this method is: - Performed in slight antibody excess, - Amenable to automation. Has two general approaches, a. Rate nephelometry b. Fixed-time nephelometry, Used for accurate measurement of IgG and IgG subclasses, IgA, IgM, C3, C4, factor B, CRP, and a number of other serum proteins. Adaptable for quantifying low-level proteins, including those in the CSF. Nephelometry is the standard method for quantifying immunoglobulin in most clinical laboratories because of the high-volume capabilities of modern nephelometers. c. Quantitative Assessment (Immunometric Methodology) 1. The radioimmunoassay (RIA): A very sensitive method. Requires expensive equipment and relatively expensive radioactive reagents, which have defined and often limited shelf-lives in addition to requiring special means for disposal. 2. ELISA: Sensitivity is almost comparable to that of an RIA. Simple to perform, requiring no radioactive isotopes, and having excellent reproducibility. Currently the standard assay in many laboratories for antiviral antibody testing e.g. HIV-ab, and also testing for a number of other immunologic proteins (including IgG subclasses, IgE, autoantibodies).
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9
Chemistry
Statistics and QC
Statistics and Quality control 22. Transport of a quantity of analyte from one specimen into a subsequent one:
a. b. c. d. e.
Carry over Sample mix up. Close system Open system Throughput.
Probable answer: Carryover. Carry over: the transport of a quantity of analyte or reagent from one specimen reaction into a subsequent one. Throughput: the maximum number of samples or tests that can be processed in an hour. Open system: Analyzer in which parameters related to an analysis can be changed and “in-house” reagents or reagents form a variety of suppliers can be used. Closed system: Analyzer requires the reagent in a unique container or format provided by the manufacturer.
23. Slow downward drifting over a month may be caused by: a. Improper blanking before standards b. Inappropriate mixing of standards. c. Standard concentration due to water evaporation. d. Standard dilution due to water accumulation. e. Wrong standard.
Probable answer: ↓concentration of standard due to water accumulation. Drift is gradual continuous movement of values in one direction over six or more analytical runs. Drift is caused by instrument or reagent instability over time, e.g. Instrument defect e.g. electronics or light source deterioration Reagent defect e.g. deterioration or concentration Inappropriateness of standards may be caused by: ↓concentration of standard due to accumulation of water causes downward drift. ↑concentration of the standard due to evaporation causes upward drift. Improper mixing of standards, a wrong standard and improper blanking of standards cause a sudden change of values from one level of the control chart to another i.e. shift.
24. A systematic error may be caused by error in: a. Blanking b. Calibrator c. Pipet d. Power supply e. Temperature changes
Probable answer: Calibrator Random errors Affect the reproducibility of precision of a test system.
Usually 13S or R4S rules. Can be due to variations in the voltage, pipettes, dispensers, contamination, volume dispensed, bubbles in lines or reagent, etc.
Systematic Errors (Bias, drifts and shifts) Recurring errors that affect the accuracy of the test system + remains constant or varies in a predictable way. Usually 22S rule ?41S or 10 x Can be due to calibration lot changes, temperature changes in incubator unit, light source deterioration, electronics, reagent lot changes, etc.
Systematic errors: Since systematic errors are due to recurring experimental condition that distorts the data every time a measurement is made e.g. a. Instrumental uncertainties that are attributable to imperfections in measuring devices, e.g. If the measuring instrument is not at zero prior to measuring b. Method uncertainties that are caused by non-ideal chemical or physical behavior of analytical systems e.g. - Improper calibration of the measuring instrument. - Errors in measurements of temperature c. Personal uncertainties that result from physical or psychological limitations of the analyst Random errors: are due to unpredictable changes e.g. in instruments or in the environmental conditions:
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11
Chemistry
Statistics and QC -
Heat loss Pipetting errors → variation in sample size. Electric power supply noise Calculation mistakes Independent analysis blank determinations
25. Which method can be used to compare the precision of two methods? a. ANOVA b. Chi squared test c. F test d. Paired t-test e. Z test
Probable answer: F test F test: to compare the precision of two analytical methods. The SDs of the methods are compared. Z test: A statistical test used to determine whether two population means are different when the variances are known and the sample size is large (z-test is preferable when n > 30) Analysis of variance (ANOVA): In its simplest form, ANOVA provides a statistical test of whether or not the means of several groups are equal, and therefore generalizes the t-test to more than two groups. ANOVAs are useful in comparing (testing) three or more means (groups or variables) for statistical significance. Paired t-Test: for comparison of methods studies. Tests the average difference of the pairs of values obtained by the candidate and reference methods. Applied to means or average differences and provides a test for accuracy or the presence of systematic errors of a method. Where n126mg/dL c. >140mg/dL d. >180mg/dL e. >200mg/dL
Anwer: 126mg/dL. Plasma glucose level: 100 - 126mg/dL in fasting sample = glucose intolerance. >126mg/dL in fasting sample diagnoses DM >140 mg/dL in postprandial sample = glucose intolerance. 180 mg is the renal threshold for glucose. > 200 in postprandial sample diagnoses DM
35. Insulin actions include: a. ↑lipolysis. b. ↑ketogenesis c. ↑protein anabolism. d. ↓permeability and glucose uptake.
Propable answer: ↑protein anabolism Physiological effects of insulin include: On carbohydrate metabolism: ↑ cell permeability to glucose and amino acids ↑ glycolysis ↑glycogen synthesis ↓gluconeogenesis On fat metabolism: ↑TG synthesis ↓ lipolysis On amino acid metabolism: ↓ protein degradation ↑protein, DNA and RNA synthesis
36. A lag curve in OGTT is due to: a. Critinism. b. Insulinoma. c. Pregnancy d. Malabsorption. e. Mild diabetes mellitus.
Probable answer: Thyrotoxicosis Alimentary glucosuria (lag storage curve) is a sharp early in blood glucose to reach a peak > renal threshold (170mg/dl) with the 2hr plasma glucose level is often much below the fasting level. Causes: - Post gastrectomy - Advanced liver disease - Thyrotoxicosis - Some apparently healthy individuals. Insulinoma, critinism, hypopitutirism and malabsorption cause flat response. Pregnancy may show gestational diabetes. Thyrotoxicosis, acromegaly show IGT or overt diabetes.
37. Gastric resection causes: a. Alimentary glucosuria b. Flat response. c. Impaired fasting glucose. d. Normal glucose tolerance. e. Renal glucosuria
Probable answer: Alimentary glucosuria Abnormalities in OGTT include: 1- DM : F ≥ 126 mg/dl, 2hr post load ≥ 211mg/dl. 2- Impaired glucose tolerance: F < 126 mg/dl, 2hr post load ≥ 141 & < 200mg/dl 3- Impaired fasting glucose : F 100-125mg/dl & 2hr post load renal threshold (170mg/dl) with the 2hr plasma glucose level is often much below the fasting level. Cause: - Post gastrectomy - Advanced liver disease - Thyrotoxicosis
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14
Chemistry
Diabetes Mellitus - Some apparently healthy individuals. 6- Flat response: Plasma glucose fails to rise significantly after an oral glucose load (the difference between the peak level & the fasting is often < 20-25mg/dl). Causes: - Malabsorption disorders - Insolinoma - Hypofunction of endocrine glands producing insulin antagonists e.g. adrenocortical hypo-secretory state ;hypopituitarism & critinism.
38. Diagnosis of DM in 36yrs old man:a. HbA1c =7% b. *FBG =126in more than 1 occasion
Probable answer: b. FBG=126 in more than one occasion. ADA diagnostic criteria of diabetes: a.
Random plasma glucose:
b.
Fasting plasma glucose
c.
2hr post load plasma glucose
≥ 200mg/dl (11.1 mmol/l) On more than one occasion Signs & symptoms of DM. ≥ 126mg/dl (7 mmol/l) on more than one occasion ≥ 211mg/dl in an OGTT on more than one occasion.
39. Blood glucose in uninhibited glycolysis sample; if left at room temperature changes by: 5-10 mg/dl/hr
Answer: 5-10 mg/dl/hr (= 50-100 mg/L/hour) Glycolysis decrease serum glucose by 5-7% in 1 hour (510mg/dL) in normal uncentrifuged coagulated blood at room temperature. The rate increases in the presence of leukocytosis or bacterial contamination. In separated, non-hemolyzed serum samples, glucose is stable for 8 hours at 25oC and 72 hours at 4oC. Sodium fluoride prevents glycolysis by inhibiting endolase, due to the formation of ionic complexes consisting of Mg2+, phosphate and fluoride ions.
40. Flat OGTT occurs in: a. malabsorption syndrome.
See Q 40
41. Renal glucosuria occurs in:
Probable answer: Fanconi syndrome Renal glycosuria: Definition: the occurrence of glycosuria although plasma glucose level is still below the renal threshold (180mg/dL) due to lowered renal threshold for glucose. It is often asymptomatic, benign condition. May be encountered in: a. Late pregnancy. b. As a part of tubular reabsorption defect e.g. Fanconi syndrome. c. Heavy metal poisoning e.g. Lead or cadmium.
42. Impaired fasting glucose:
100-126 mg/dL. See Q 34
43. Diabetic ketoacidosis all may be true except: a. Positive ketone b. Negative glucose in urine c. K+ 6.5 d. pH 7.5
Probable answer: pH 7.5 The most widely used criteria to diagnose DKA are: 1. plasma glucose above 200–250 mg/dL (11.1–13.9mmol/L; cutoff varies depending on recommendation followed), Concentrations rarely exceed 800 mg/dL in DKA, although they may be higher in hyperosmolar hyperglycemic states (HHSs). 2. serum bicarbonate ≤15 mEq/L, 3. arterial blood pH ≤ 7.30, and 4. ketones in the urine or blood: ↑serum ketone concentrations are not always detected in DKA by routine assays. However, patients almost always have an increased anion gap, which provides indirect evidence that ketoacids are present
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15
Chemistry
Diabetes Mellitus NB:
44. The renal threshold for glucose is__________________. a. 180 mg/dl b. 160 mg/dl c. 140mg/dl d. 120 mg/dl
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Hyperkalemia and hyperphosphatemia are other frequent findings in DKA. Glycosuria may be absent in long standing DM due to increased renal threshold. Hyperosmolar hyperglycemic states (HHS), in contrast, is more common among type 2 diabetic patients and rarely results in ketonemia or an increased anion gap. The incidence of DKA is greatest in children with type 1 diabetes, followed by adults with type 1 diabetes, and is least common in patients with type 2 diabetes. Although a history of type 1 diabetes raises the suspicion of DKA, it is not required because DKA is present in 15–67% of children at the time of initial diagnosis of type 1diabetes. DKA is sometimes further classified as mild, moderate, and severe according to arterial blood pH, plasma bicarbonate concentration, and CNS symptoms and signs.2
Answer: 180mg/dL. The renal threshold for glucose is the plasma level at which the glucose first appears in the urine in more than the normal minute amounts. Predicted renal threshold: about 300 mg/dL, that is, 375 mg/min (Transport maximum for glucose TmG) divided by 125 mL/min (GFR). Actual renal threshold is about 200 mg/dL of arterial plasma, which corresponds to a venous level of about 180 mg/dL. This is difference is because glucose starts to appear in the urine at the threshold before the transport maximum is reached since not all nephrons have the same transport maximum for glucose, and some of the nephrons excrete glucose before others have reached their transport maximum.
16
Chemistry
Lipids
Lipids 45. The lipoprotein that is found in biliary obstruction:
Probable Answer: LpX Lipoprotein4 LpX is an abnormal lipoprotein found in patients with obstructive biliary disease, and in patients with familial lecithin/cholesterol acyltransferase (LCAT) deficiency. Lipids account for more than 90% of its weight (mostly phospholipids, unesterified cholesterol, and very little esterified cholesterol), while proteins, primarily apoC and smaller amounts of albumin, constitute 500
Probable answer: High apolipoprotein B-100 LDL 2mg/dL) due to parenchymal inflammation and edema interfere with bilirubin conjugation and with bile excretion. Manifestations: Jaundice and dark urine (++conjugated bilirubin) and clay-colored stools Hepatic enlargement and tenderness. C. Recovery stage. Characteristic investigations in acute hepatitis: 1. AST & ALT: Typically elevated during the final weeks of the incubation period in viral hepatitis Usually the first abnormal biochemical tests regardless of the causative agent. Enzyme elevations typically peak before peak bilirubin occurs, and remain increased for an average of 4 to 5 weeks (longer for ALT than AST because of its longer half-life) 10- 100 times of normal values Probably viral hepatitis. < 10 times of normal may suggest a non viral etiology. ALT is typically higher than AST because of slower clearance. 2. Urine bilirubin: detected before appearance of jaundice. 3. Serum bilirubin: start to elevate during prodromal phase. 4. Hypoalbuminemia is present only in chronic hepatitis as the half life of albumin is 21 days.
106. Blood ammonia is used for the assessment of: a. Hepatic cell failure. b. Obstructive jaundice. c. Zollinger Ellison syndrome. d. Hepatoma e. Liver maturity in neonates.
Probable answer: Hepatic cell failure Most ammonia is formed by breakdown of proteins bacteria in the intestines. The liver normally converts ammonia into urea. Ammonia levels in the blood rise when the liver is not able to convert ammonia to urea. Indications: The fasting venous plasma ammonia concentration is useful in:
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34
Chemistry
Liver I)
Acquired causes of hyperamrnonemia: - Advanced liver disease: Severe or chronic liver failure e.g. fulminant hepatitis and cirrhosis, respectively). - Renal failure. Blood ammonia determination helps to: a. Assess hepatic sufficiency and predict prognosis of acute liver failure. b. Check success of treatment for severe liver disease. II) Heridetary causes of hyperammonemia: - Reye syndrome: primarily a CNS disorder with minor hepatic dysfunction. - Inherited disorders of urea metabolism. Blood ammonia determination helps to: a. Newborn with symptoms such as irritability, vomiting, lethargy, and seizures arise in the first few days after birth. b. A child develops such symptoms about a week following a viral illness, such as influenza or a cold. NB Sources of preanalytical error: (1) Contamination (from cigarette smoke, use of ammonium heparin anticoagulation), (2) Collection process (prolonged tourniquet use, fist clenching during collection), (3) Sample handling (delayed analysis, failure to put sample in ice water). In obstructive jaundice, Zollinger Ellison syndrome and hepatoma the hepatic conversion of ammonia to urea is not affected. Liver immmaturity in neonates is related to hyperbilirubinemia and inadequate protein formation e.g. coagulation factors.
107. The earliest enzyme that indicates recovery from acute liver disease is: a. 5 NT b. ALP c. ALT d. AST
Probable answer: AST. The most common alterations in hepatic enzymes can be divided into 2 major subgroups: 1. Hepatocellular predominant: - ALT, AST & ALP: are the most useful - GGT, 5'NT & Glutathion S transeferase: are less useful. 2. Cholestatic predominant: - GGT, ALP and 5NT are more useful NB certain liver diseases may display a mixed biochemical picture (usually elevated AST and ALT levels with mild abnormalities of ALP and GGT levels). In direct injury, there is typically a rapid rise in cytosolic enzymes, such as AST, ALT, and LD, followed by a rapid fall with rates of decline similar to known half-lives of the enzymes. All forms of acute viral hepatitis have a similar clinical course, with marked elevations in aminotransferases, usually between 8 and 50 times the upper reference limits. ALT is typically higher than AST because of slower clearance. Enzyme elevations typically peak before peak bilirubin occurs, and remain increased for an average of 4 to 5 weeks (The half-life in the circulation is about 47 hours for ALT, about 17 hours for total AST and, on average, 87 hours for mitochondrial AST.).
108. the most sensitive test for mild liver cirrhosis is: a. ALT. b. AST.
Probable answer: ALT Being cytoplasmic, ALT is more sensitive in early, acute and obstructive liver diseases. Being mitochondrial, AST is more sensitive in late, chronic and malignant liver diseases.
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35
Chemistry
Liver
109. Dubin-Johnson
Probable answer: Conjugated hyperbilirubinemia. Dubin Johnson & Rotor syndromes: Incidence: Rare, benign conjugated hyperbilirubinaemia and bilirubinuria. Cause: Genetic (autosomal recessive) defect in the transfer of conjugated bilirubin into the biliary canaliculi (defect in bilirubin excretion) due to deficiency of transport globulins.
110. In Rey' syndrome all are true except: a. elevated serum bilirubin. b. elevated liver enzymes. c. increase ammonia.
Probable answer: a. elevated serum bilirubin
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Reye's syndrome Definition: Acute encephalopathy in combination with fatty degeneration of the viscera.
36
Chemistry
Liver
Lab finding: AST & ALT Total bilirubin Ammonia (encephalopathy). AAs & FFAs UA PT Glucose
↑ (especially ALT). N or slight ↑ ↑ Hyper-aminoacidemia Hyperuracemia (Hypoprothrombinemia unresponsive to vitamin k) Tendancy to hypoglycemia in young age
- Liver biopsy is diagnostic.
111. Neonatal unconjugated hyperbilirubinemia: a. Gilbert , b. Dubin Johnson, c. Crigler Najjar, d. Rotor
Probable anser: c. Crigler-Najjar. Crigler-Najjar syndrome: A rare neonatal hyperbilirubinemia due to UDP-GT Type I (severe form) Complete absence of UDP-GT Severe, hyperbilirubinaemia in neonate total bilirubin 20-50 mg/dl Causes Kernicterus
Type II (moderate form) Moderate reduction in the level of UDP-GT Total bilirubin < 20 mg/dl The condition depends on the level of enzyme reduction.
Gibert, although unconjugated, is usually detected in adolescence Dubin Johnson and Rotor’s syndromes cause conjugated hyperbilirubinemia.
112. In precore HBV all true except:
Probable answer: HBeAg positive A precore mutant is a variety of hepatitis B virus that does not produce hepatitis B virus e antigen (HBeAg). These mutants are important because infections caused by these viruses are difficult to treat, and can cause infections of prolonged duration and with a higher risk of liver cirrhosis. The HBV has four genes: Codes for HBsAg S Codes for DNA polymerase P Codes for HBeAg and HBcAg C Has precore (produces HBeAg) and core region (produces HBcAg) codes for HBxAg which may be involved in carcinogenesis X Precore mutants are readily detectable by HBV DNA in serum, but hepatitis B e antigen (HbeAg) is absent. The X gene.[6]
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37
Chemistry
Liver
Remember: HBsAg: - Used for diagnosing acute infection or detecting carriers. - First viral marker to appear during acute infection. - Its persistence >6 months typically characterizes the state of chronic carrier. - Its presence indicates that a person is infectious. HBsAb or anti-HBs (protective, neutralizing Ab) - A marker of recovery or immunization. - Its presence, in absence of other +ve serologies, is seen in successfully immunized individuals. anti-HBc: - A combination of IgG and IgM antibodies. - It develops in all HBV infections and indicates infection at some undefined time in the past. - It generally persists for life, - Not a marker for acute infection, - Does not develop from vaccine. IgM anti-HBc: - Appears in persons with acute disease and tends to disappear several weeks after initial exposure. - A marker of acute infection although it can also be seen during flares or exacerbation of chronic HBV. HBeAg (marker of replication and infectivity): - Its absence does not ensure that there is no replication or infectivity as in the precore mutant strain of HBV, which does not produce HBeAg, but it still successfully replicates. HBeAb or anti-HBe: Appears when infected individuals lose HBeAg (seroconversion). This is often associated with the disappearance HBV DNA in serum and remission of liver disease. HBV DNA (marker of replication and infectivity). - Can be detected and quantified by using a nucleic acid test (NAT). - Used to determine the need for treatment and to assess the response to therapy.
Interpretation of the Hepatitis B Panel HBsAg Anti-HBc Anti-HBs HBsAg Anti-HBc Anti-HBs HBsAg Anti-HBc Anti-HBs HBsAg Anti-HBc Anti-HBs HBsAg Anti-HBc IgM anti-HBc Anti-HBs HBsAg Anti-HBc Anti-HBs
Negative Negative Negative Negative Positive Positive Negative Negative Positive Positive Positive Positive Positive Positive Negative Negative Negative Positive Positive
Susceptible
Immune due to natural infection Immune due to hepatitis B vaccination Acutely infected
Chronically infected
Either: 1. Recovering from acute HBV infection. 2. Distantly immune and test not sensitive enough to detect very low level of anti-HBs in serum. 3. Susceptible with a false-positive antiHBc. 4. Undetectable level of HBsAg present in serum and the patient is actually a carrier.
113. severity of chronic liver disease is indicated by a. S. albumin b. ALP c. GGT
Probable answer: a. Serum albumin S. Albumin: a marker for synthetic function of the liver; it is valuable guide to the severity of chronic liver disorders. Low S. albumin is bad prognostic sign.
114. Feces gets its brown pigmentation from_____. a. stecobilirubin b. stercobilin c. stercobilinogen d. stecobilin
Probable answer: d.stercobilin Conjugated bilirubin is excreted in urine as urobilinogen, giving urine its color. In the intestine, bilirubin is converted by bacteria to stercobilinogen. Stercobilinogen is oxidized to stercobilin, which is responsible for the pigmentation of feces.
115. In a hemolytic crisis, bilirubin is: a. normal b. increased c. decreased d. unchanged
Probable answer: Increased.
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38
Chemistry
Enzymes
Enzymes 116. Hyperamylasemia not a feature of a. Acute pancreatitis. b. Cerebral trauma. c. Cystic fibrosis. d. Intestinal obstruction. e. Perforated peptic ulcer.
Probable answer: Cystic fibrosis Hyperamylasemia occurs in: 1. Acute pancreatitis: within 2 hours, peak 12-72 hrs and ↓4days. The increase is not corresponding to severity, but the higher the level the higher the probability of pancreatitis. 2. Complications of acute pancreatitis: Persistantly high amylase pseudocyst of pancrease. 3. Other causes of acute abdomen: Appencdicitis Intestinal obstruction Peptic ulcer perforation Peritonitis. Salpingitis, ectopic pregnancy 4. Salivary fraction: in parotitis, mumps, calculi etc. 5. Renal insufficiency due to excretion. 6. DKA. 7. Addicts spasm of sphincter of Oddi. Other causes of hyperamylasemia include pneumonia (↑salivary amylase), cerebral trauma (activate pathways that increase amylase levels in the blood, suggesting a central nervous system regulation of serum amylase levels), burns, abdominal aortic aneurysms (increased pancreatic amylase), drugs (increased salivary and/or pancreatic amylase), anorexia nervosa and bulimia (increased salivary amylase), nonpathologic (increased salivary and/or pancreatic amylase), and organophosphate poisoning In Cystic fibrosis, blood levels of amylase may rise when mucus blocks the pancreatic ducts from carrying the enzymes that the small intestine needs to digest food properly.
117. An enzyme that is located exclusively in cytoplasm is: a. Acid phosphatase. b. AST c. Glutamate dehydrogenase. d. Isocitrate dehydrogenase e. LDH.
Probable answer: LDH or ALT A mild, reversible viral inflammation of the liver is likely to increase only the permeability of the cell membrane and allow cytoplasmic enzymes to leak into the blood. A severe attack causing cell necrosis also disrupts the mitochondrial membrane, and both cytoplasmic and mitochondrial enzymes are detected in blood. Thus knowledge of the intracellular location of enzymes helps to determine the nature and severity of a pathological process if suitable enzymes are assayed in the blood. Acid phosphatase is present in lysosomes, which are organelles present in all cells with the possible exception of erythrocytes.Extra lysosomal ACPs are also present in many cells. CK: there are 3 cytosolic isoenzymes (CK-3, CK-2, CK-1) and one mitochondrial isoenzyme (CK-Mt) Glutamate dehydrogenase: glutamic dehydrogenase is found in the nucleus as well as in the cytoplasm (at 60% of the cytoplasmic level). LDH activity is present in all cells of the body and is invariably found only in the cytoplasm of the cell. AST: both mitochondria1 and cytoplasmic forms are found in cells. GGT is present in cytoplasm (microsomes), but the larger fraction is located in the cell membrane. ALT is exclusively cytoplasmic; Isocitrate dehydrogenase is found in the cytoplasm and peroxisomes. - enzymes that catalyze the oxidative decarboxylation of isocitrate to 2-oxoglutarate.
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39
Chemistry
Enzymes - Belong to two distinct subclasses, one of which utilizes NAD(+) as the electron acceptor and the other NADP(+). - Five isocitrate dehydrogenases have been reported: three NAD(+)dependent IDH, which localize to the mitochondrial matrix, and two NADP(+)-dependent isocitrate dehydrogenases, one of which is mitochondrial and the other predominantly cytosolic. - Each NADP(+)-dependent isozyme is a homodimer. - The protein encoded by the IDH2 gene is the NADP(+)-dependent isocitrate dehydrogenase found in the mitochondria. - It plays a role in intermediary metabolism and energy production. This protein may tightly associate or interact with the pyruvate dehydrogenase complex. NTP is a glycoprotein widely distributed throughout the tissues of the body and is principally localized in the cytoplasmic membrane of the cells in which it occurs
118. In acute abdomen all can occur except: a. Hypoamylasemia
Hyperamylasemia: occurs in 70-75% of cases of acute pancreatitis (the higher the more probable the diagnosis), however, isoenzymes and urine amylase are more specific than the total and serum amylase respectively. parotitis, renal insufficiency (↓excretion) other causes of acute abdomen e.g. appendicitis, intestinal obstruction, peptic ulcer perforation, peritonitis, salpingitis or ectopic pregnancy. Hypoamylasemia may occur in chronic pancreatitis associated with irreversible damage to pancreas.
119. The enzyme with shortest half life: a. LD5. b. ALT. c. Intestinal ALP.
Probable answer: AST then ALT or CK then LD Clearance of enzymes from plasma occurs at variable rates. The half life of an enzyme causes variation in the duration of elevation of the enzyme after release in the circulation. So, roughly to answer such a question, remember which enzyme disappears earliest among the profile and which disappears last e.g. CK has a shorter half life than LDH, More precisely: The half-life of ALT is 47 hours, The half-life of cytosolic AST is 17 hours; thus although more AST is released from liver, the much longer half-life of ALT leads to higher activities of ALT than AST in most forms of hepatocellular injury. The half-life of the liver isoenzyme of ALP is from 1 to 10 days; the former figure appears to correspond better to the changes seen with removal of gallstones. The half-life of GGT is 4.1 days. The half-life of CK-MB in the circulation is relatively short (approximately 12 hours)
120. The enzyme needed in biological systems for joining two molecules is called: a. Lyases b. Diastases c. Polymerases d. Hydrolase
Classification of enzymes:Enzyme commission (EC) classification: 1. Oxidoreductases: (dehydrogenases or oxidases) AH2 + B A + BH2 a. Aerobic oxidases: (use oxygen as H2 acceptor) AH2 + O H2O +A e.g. tyrosinase and cytochrome oxidase. b. Aerobic dehydrogenases: (H2O2 is formed) AH2 + O2 H2O2 + A e.g. glucose oxidase. c. Anaerobic dehydrogenase: (need coenzyme acceptor) AH2 + coenzyme coenzyme H2 + A e.g. LDH need NAD, G-6-PD need NADP. Importance: of particular importance in: a) Direct diagnostic value.
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41
Chemistry
Enzymes b)
2.
3.
4. 5. 6.
Coupling reactions: Dehydrogenases can be used as indicator enzymes for measuring activities of other enzyme which do not involve oxidation or reduction. Transferases: transfer a group from one compound to another e.g. Aminotransferases AST, ALT transfer amino group. Phosphotransferases CK transfer phosphate group. Hydrolases: Hydrolyze the substrate. A-B + H2O AH + BOH According to their substrates they include: a.Hydrolases acting on esters: Lipase, choline esterase, phosphatases, ALP, ACP,5-nucleotidase,glucose-6phosphatase. b. Hydrolases acting on glycosyl compounds: -amylase. c. Hydrolases acting on peptide bonds: Pepsin. d. Hydrolases acting on C-N bond: e.g. urease. Lyases: Remove a chemical group from substrate by mechanism other than hydrolysis e.g. aldolase. Isomerases: Inter-convert optical isomers e.g. racemases and epiderases. Ligases: (synthases): Link 2 molecules together and need ATP e.g. acetyl-co-A synthase.
NB: Polymerases: are enzymes that catalyse the synthesis of a polymer, esp the synthesis of DNA or RNA. Diasterases: are enzymes that break down starch into maltose and dextrose.
121. Which of the following enzymes is most specific for diagnosis of a Myocardial Infarction? a. AST b. LD c. Troponin. d. CK
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Probable answer: CK (being an enzyme) or Troponin (being most specific) Biochemical markers of myocardial injury: 1. Aspartate aminotransferase: was considered as a very good marker of cardiac injury as it was found to be normal in pulmonary embolism acute abdominal conditions and other heart conditions such as angina and pericarditis. But later on, its use become limited due to its elevation in trauma to skeletal muscles and liver diseases 2. Lactate dehydrogenase and its isoenzyme LD1: The prolonged elevation makes it a good marker for those patients admitted to the hospital after several days of MI. However, its use is discouraged due to its non-specificity as its increased levels are found in progressive muscular dystrophy, myoglobinuria, leukaemia, pernicious anaemia, megaloblastic and hemolytic anaemia, renal disease and in generalized carcinoma 3. Creatine kinase and its isoenzyme MB: its presence in large amounts in skeletal muscle and increased levels found in muscular dystrophy, hypothyroidism, hypothermia, alcoholism, cerebrovascular accidents and a variety of myopathies make it unsuitable as a marker of myocardial injury. Recently, the measurement of mass concentration of CKMB has increased its sensitivity and specificity enabling tomeasure small changes during the early hours following MI 4. Myoglobin: a 18 KD cytosolic protein, appears in blood earlier after myocardial injury than any other marker available so far. However, it is not cardiac specific as its release from the skeletal muscles cannot be distinguished from that released due to cardiac injury (36) and it is found to be elevated in severe renal insufficiency and
41
Chemistry
Enzymes
5.
in patients being on alcohol. Cardiac Troponins: a protein complex located on the thin filament of striated muscles consisting of the three subunits namely Troponin T (TnT), Troponin I (TnI) and Troponin C (TnC). Of the three troponins, TnT and TnI are being used as the biochemical markers for the diagnosis of myocardial injury. The troponins found in cardiac tissue (cTn) have a different amino acid sequence than that present in troponin of skeletal muscles. This makes cTnT and cTnI more specific for the diagnosis of myocardial injury. cTnT and cTnI are now regarded as the most specific biochemical markers of myocardial injury.
122. ALP is elevated in the following disorder? a. Addison's Disease. b. Paget's Disease c. Diabetes Insipidus d. Scleroderma
Probable answer: b. Paget’s disease. The highest levels of ALP (10-25 times the URL) are encountered in Paget’s disease as a result of the action of the osteoblastic cells as they try to rebuild bone that is being resorbed by the uncontrolled activity of osteoclasts
123. The "MM" fraction of CK is most abundant in _____z a. Skeletal muscle b. Cardiac muscle c. Brain tissue d. none of the above
Probable answer: Skeletal muscle According to the type of subunits, CK has 3 isoenzymes: 1. CK1 (BB): Specific for the brain. The fastest in electrophoresis and moves towards the anode. 2. CK2 (MB): Specific for myocardium. Normally, CK-MB activity is < 5U/L and accounts for 290mosmol/Kg DI = (deficient ADH) can result from 1. ADH deficiency. 2. ADH resistance: Renal tubular disease. Nephrogenic DI 3. Central (hypothalamic, neurogenic, cranial DI ) Any destructive hypothalamic or infundibular lesion (80 % of ADH secreting neurones ) DI is characterized by: - Polyuria >2.5L/day - Low urine Sp. Gr.(1st morning sample) 290 mosmol/Kg. b. ++ vasopressin. c. ↓ sodium. d. Sp.G >1030 e. Thirst center abnormality.
136. In panhypopituitrism following is decreased: a. Aldosterone b. Cortisol c. Estrogen d. TSH e. ADH
the
Probable answer: TSH or cortisol. Panhypopituitarism is a condition of inadequate or absent production of the anterior pituitary hormones.
Insufficient Hormones Insufficient levels of gonadotropins. Insufficient levels of growth hormone. Insufficient levels of thyroid-stimulating hormones. Insufficient corticotrophic levels. Excessive prolactin levels.
e. Reproduction 137. A hormone decreased in woman pregnant with a fetus having Down syndrome a. E3 b. E2 c. hCG d. Progesterone
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Probable answer: Estriol (E3) A number of tests can be used for screening pregnant women for fetus with Down syndrome with varying levels of accuracy and invasiveness. Maternal serum AFP and E3 and pregnancy-associated plasma protein-A (PAPP-A) are lower in Down syndrome than in unaffected pregnancies while CG is increased about twice as high. While E3 is only produced in significant amounts during pregnancy as it is made by the placenta, estradiol (E2) is produced by the ovaries and is used to measure primarily the activity of the ovaries.
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Chemistry
Hormones First and second trimester screening Weeks gestation
Screen
Description
Combined 10–13.5 wks test
- US to measure nuchal translucency (NT) - Free or total β-hCG - APP-A.
Quad screen
AFP Unconjugated estriol, hCG, Inhibin-A.
15–20 wks
Negrated 15-20 wks test
Quad screen + PAPP-A, and NT
138. In post menopausal women continual elevation of:
Probable answer: FSH Menopause Definition: the permanent cessation of menstruation resulting from loss of ovarian follicular activity. Hormonal changes: Oestrogen and FSH: The ovaries fail to produce adequate amounts of estrogen and inhibin → ↑gonadotropin production to stimulate the ovary. Perimenenopausal changes: Hormonal changes begin about 5 years before the actual menopause, as the response of the ovary to gonadotropins begins to decrease, and menstrual cycles become increasingly irregular. This transition phase has been observed to last from 2 to 8 years.' At this time, FSH concentrations increase and estradiol concentrations decrease. β-CG concentrations: It has been occasionally observed that postmenopausal women have slightly elevated β-CG concentrations (typically >5 but 1.75 μg/L/yr) occur in patients with prostate cancer. - Uusing PSA and other analytes to increase the sensitivity of prostate cancer detection.. Staging of Prostate Cancer Higher PSA concentrations are associated with more advanced stages. PSA concentration can serve as a guide and is more useful in evaluating the presence of metastases: PSA≥ 50 pg/L → most likely to have extracapsular tumor PSA
