Medical Lab Science Exam Prep #19: Analytes, Methods, and Errors

MEDICAL LABORATORY SCIENCE SUMMATIVE EXAM REVIEW QUESTIONS #19 + ANSWERS & RATIONALIZATIONS 1. 2. 3. 4. 5. 6. 7. 8. Which assay using 24-hour urine is considered the best single screening test for pheochromocytoma? a. Total urinary catecholamines b. VMA c. Homovanillic acid (HVA) d. Metanephrines → Measurement of 24-hour urinary metanephrine is about 95% sensitive for pheochromocytoma, and is the best single test. Urinary HVA is most often assayed to detect: a. Pheochromocytoma b. Neuroblastoma c. Adrenal medullary carcinoma d. Psychiatric disorders such as manic depression Which of the following would not be a typical analyte in a clinical chemistry test? a. Calcium b. Protein c. Octane d. Cocaine Which of the following would be a typical analyte in a clinical chemistry test? a. Calcium b. E. coli positivity c. Octane d. Food additives What type of additive is in a blood collection tube with a red cap? a. Lithium or sodium heparin b. Potassium EDTA c. Thrombin d. No additive How should a laboratory verify the reference range it uses for a particular test? a. Call another laboratory b. Use the numbers from a textbook c. Test samples from healthy people d. Look on a medical internet site Typically, a patient test result that EXCEEDS 3 SD of the mean value for analyte is found with a frequency of: a. 1 in 5 b. 1 in 20 c. 1 in 100 d. Never → 2 SD: five out of every hundred healthy people would be expected to have a test result outside of the reference interval — either high or low → 3 SD: one out of every hundred healthy people would be expected to have a result outside the reference interval. → Most chemistry tests use 2 SD reference intervals. Potentiometric methods are most useful for which of the following types of analytes? a. Proteins b. Electrolytes c. Drugs of abuse d. Lipids 9. In a test for albumin, all the albumin reacts very rapidly with an excess of the dye bromocresol purple (BCP) to produce a colored complex. The detector is set to measure the product complex. What method is most suitable for this determination of albumin? a. Endpoint (end-up) → creation of a product b. Endpoint (end-down) → disappearance of product c. Rate (rate-up) → appearance of product d. Rate (rate-down) → disappearance of substrate 10. Transferrin reacts with a specific antibody to produce immune complexes. What method would be most suitable to measure the concentration of transferrin? a. Immunoturbidimetry b. Fluorescence c. Potentiometry d. None of the above 11. What is the best estimate of concentration of substance J in a sample whose absorbance is 0.50? a. Between 1 and 2 nmol/L b. Between 2 and 3 nmol/L c. Between 3 and 4 nmol/L d. Greater than 4 nmol/L 12. When a serum sample has intrinsic color that absorbs at the same wavelength used to detect the reaction product, what technique could help distinguish the color produced by the analyte from the intrinsic color of the sample? a. Blanking b. Immunoturbidimetry c. Ion-selective electrode d. PETINIA (Particle-Enhanced Turbidimetric Inhibition Immunoassay) 13. Which of the following analyses would best be done using a photometric rate reaction? a. Measurement of lipase activity b. Determination of albumin with the dye bromocresol green c. Determination of potassium in the presence of excess sodium d. None of these could be done using a rate reaction 1 14. Pretreatment is designed to do which of the following? a. Ensure the concentration of analyte is in the measurable range b. Remove substances that could be erroneously measured as analyte c. Adjust the wavelength of light used for analysis d. Introduce a fluorophore 15. Which of the following would NOT be a typical methodology for a clinical chemistry test? a. Immunoturbidimetry b. Microscopy c. EMIT® (Enzyme-Multiplied Immunoassay Technique) d. ISE 16. Which of the following sets of values for repeat analyses of a QC sample (target value of 50) reflects the best precision? a. 50, 51, 52 b. 50, 52, 56 c. 48, 50, 52 d. 44, 50, 53 17. Which of the following sets of values for repeat analyses of a sample (target value of 100) shows the least bias? a. 100, 105, 110 b. 95, 100, 105 c. 90, 95, 100 d. 90, 100, 105 → Bias is usually described as a percent reflecting the difference between the measured value and the true value. 18. Method A and Method B for cholesterol both give a value of 200 mg/dL for a serum sample; however, the same QC material analyzed by Method A gives 185 mg/dL and by Method B gives 212 mg/dL. What might cause this? a. Method B is biased b. Method A is imprecise c. Both methods are showing a matrix effect for the QC material d. Any of the above answers may be correct → When the addition of extra substances, freezing or lyophilization alters the solution properties in a way that biases the measured result, the bias is said to result from a “Matrix Effect.” → Matrix Effects: Interference effect of a sample matrix causing a false decrease or increase in a test result; common matrix interferents are hemolysis, icterus and lipemia. 19. What does method traceability mean? a. The calibration of a method is linear b. The method meets the required error budget c. The method’s accuracy is linked to a certified method and/or material d. The method does not show matrix effects 20. Which of the following analytes has the biggest allowable error budget based on CLIA accuracy ranges? a. Albumin b. Triglycerides c. Chloride d. Cholesterol → 21. 22. 23. 24. 25. 26. 27. 28. The biologic variation is taken into account when setting the “Error Budget” or Total Error Allowable (TEa) for a laboratory test. → The TEa is the amount a test result may deviate from the “true value” and still be acceptable. Which of the following is an example of a preanalytical error? a. Test method incorrectly calibrated b. Collection of blood in wrong kind of tube c. Presence of interfering substance in specimen d. Delay in sending the report to the provider Which type of analytical error can be prevented by a good quality control program? a. Instrument not properly calibrated b. Presence of interfering substances in sample c. Presence of bubbles in the light path of a photometric method d. Analyte concentration so high it depletes the active reagent Which type of analytical error is recognized by an HIL index? a. Instrument not properly calibrated b. Presence of interfering substances in sample c. Presence of bubbles in the light path of a photometric method d. Analyte concentration so high it depletes the active reagent e. HIL: Hemolysis, Icterus and Lipemia; the most common interferents found in blood specimens. What option(s) might be employed if a test result is above the upper limit of the test measurement range? a. Manual dilution followed by reanalysis of the diluted sample b. Automatic dilution and reanalysis of the sample c. Use of a reaction rate algorithm using two read windows for an enzyme assay d. Reporting the result as higher than the upper limit of the test method e. All of these Which of the following tests is a good marker of nutritional status? a. Immunoglobulin M b. Prealbumin c. Ceruloplasmin d. Lp(a) Which test might be used to assess a person who is disoriented or confused? a. Cholesterol b. Ammonia c. CRPs d. Iron Which tests might be ordered on a patient with abdominal pain to test for possible pancreatitis? a. Amylase and lipase b. Sodium and potassium c. Cholesterol and triglyceride d. C3 and C4 Which of these drug levels would be considered toxic? a. Alcohol at 80 mg/dL b. Valproic acid at 50 μg/mL c. Digoxin at 2 ng/mL d. Acetaminophen at 250 μg/mL e. Salicylate at 27 mg/dL 2 → 29. 30. 31. 32. 33. 34. 35. Important Substance Values: ▪ Therapeutic • Valproic acid: 50–100 μg/mL (346–693 μmol/L) • Digoxin: 0.8–2 ng/mL (1–2 .6 nmol/L) ▪ Toxic Values for Ethanol • Impairment: 50–100 mg/dL (11–22 mmol/L) • Depression of CNS: > 100 mg/dL (> 21 .7 mmol/L) • Fatalities reported: > 400 mg/dL (> 86 .8 mmol/L) ▪ Acetaminophen: > 200 μg/mL (> 1,324 μmol/L) ▪ Salicylate: > 500 μg/dL (> 3 .62 μmol/L) Which test is used as an indicator of congestive heart failure? a. CRP b. BNP c. Cholesterol d. Troponin e. Haptoglobin Which of the following tests is the best monitor of diabetic glucose control over an 8–12-week period? a. Glucose b. Urine microalbumin c. Hemoglobin A1c d. Haptoglobin The lipoprotein particle that is used to determine increased risk of coronary artery disease and to determine and monitor treatment for high cholesterol is: a. HDL b. LDL c. Apolipoprotein A1 d. Chylomicron Which test is the most specific for myocardial infarction? a. LDH b. CK c. Troponin d. Myoglobin If a screening TSH is high, which test is likely to be ordered next? a. Cholesterol b. Free T4 c. Ferritin d. Glucose In which condition would TIBC be high? a. Hemochromatosis b. Chronic illness c. Malnutrition d. Iron deficiency When the kidneys are not functioning properly to filter blood and rid the body of wastes, which of these test results would be most likely? a. GFR = 100 mL/min b. High blood creatinine c. High blood albumin d. Low blood BUN 36. Which of the following units would not be used for reporting glucose on a clinical chemistry laboratory report? a. mg/dL b. ounces/L c. mmol/L d. All are acceptable units 37. What would be the value of 150 mg/dL glucose reported in SI units? a. 1.61 mmol/L b. 8.25 mmol/L c. 0.367 mmol/L d. None of the above values → Conversion factor: 0.0555 38. If total cholesterol is 4.0 mmol/L, what is the value in conventional units? a. 154 mg/dL b. 102 mg/dL c. 40 mg/dL d. None of the above values → Conversion factor: 0.026 39. If the enzymatic activity of LD is 40 IU/L at 25°C, what is the activity at 37°C? a. 40 IU/L b. 59 IU/L c. 27 IU/L d. Impossible to tell from information provided → Enzymatic activities reported in the same units cannot be compared if tested under different reaction conditions. 40. Composition of Gower’s diluent: a. Acetic acid, sodium sulfate, water b. Citrate, formaldehyde c. Mercuric chloride, sodium sulfate, sodium chloride d. Sodium chloride, water 41. 1:200 dilution of a patient’s sample was made and 336 red cells were counted in an area of 0.2 mm2. What is the RBC count? a. 1.68 × 1012/L b. 3.36 × 1012/L c. 4.47 × 1012/L d. 6.66 × 1012/L → The formula used for calculating manual cell counts using a hemacytometer is: 42. A manual WBC count is performed. Eighty WBCs are counted in the four large corner squares of a Neubauer hemacytometer. The dilution is 1:100. What is the total WBC count? a. 4.0 × 109/L b. 8.0 × 109/L c. 20.0 × 109/L d. 200.0 × 109/L 43. A manual white blood cell (WBC) count was performed. A total of 36 cells were counted in all 9mm2 squares of a Neubauer-ruled hemacytometer. A 1:10 dilution was used. What is the WBC count? a. 0.4 × 109/L b. 2.5 × 109/L c. 4.0 × 109/L d. 8.0 × 109/L 3 44. An adult has a total white blood cell count of 4.0 X 109/L (4.0 X 103/µL). The differential count is as follows: polymorphonuclear neutrophils (PMNs) 25%, bands 5%, lymphocytes 65%, and monocytes 5%. The absolute value reference range for lymphocytes is 1.0 to 4.0 X 109/L. Which of the following is true? a. The percentage of lymphocytes is normal. b. There is an absolute lymphocytosis. c. There is a relative lymphocytosis. d. There is both an absolute and a relative lymphocytosis. → Lymphocytes make up between 18% and 42% of circulating leukocytes with an absolute number of 0.8 to 4.8 X 109/L. 45. A 19-year-old man came to the emergency department with severe joint pain, fatigue, cough, and fever. Review the following laboratory results: WBCs 21.0 × 109/L RBCs 3.23 × 1012/L Hgb 9.6 g/dL PLT 252 × 109/L Differential: • 17 band neutrophils • 75 segmented neutrophils • 5 lymphocytes • 2 monocytes • 1 eosinophil • 26 NRBCs What is the corrected WBC count? 50. In ELISA, which of the following can be attached to a solid-phase support (e.g. polystyrene)? a. Antigen and enzyme b. Antibody and albumin c. Antigen and antibody d. Antigen and albumin 8.1 × 109/L 16.7 × 109/L 21.0 × 109/L 80.8 × 109/L Corrected WBC Count: Uncorrected WBC count x 100 100 + nucleated RBCs In the Sanford Method of OFT, normal RBCs demonstrate initial hemolysis at which tube? a. 14 b. 17 c. 20 d. 22 In the Sanford Method of OFT, normal RBCs demonstrate complete hemolysis at which tube? a. 14 b. 17 c. 20 d. 22 The reference value for mean platelet volume (MPV) is approximately: a. 2 to 4 fL b. 5 to 7 fL c. 8 to 10 fL d. 11 to 14 fL A normal PDW is: a. Less than 5% b. Less than 10% c. Less than 15% d. Less than 20% → The PDW is a measure of the uniformity of platelet size in a blood specimen. This parameter serves as a validity check and monitors false results. A normal PDW is less than 20% a. b. c. d. → 46. 47. 48. 49. 4