CLS Clinical Chemistry 1 — Questions and Answers
Question 1: Which specimen is preferred for most clinical chemistry tests to avoid interference from cellular components?
- Whole blood collected in EDTA
- Serum or plasma separated from cells (Correct answer)
- Urine collected over 24 hours
- Cerebrospinal fluid collected by lumbar puncture
Correct answer: Serum or plasma separated from cells
Serum or plasma is preferred for most clinical chemistry tests because cellular components can interfere with analyte measurement and enzymatic reactions.
Question 2: A patient's serum glucose is measured at 350 mg/dL. Which method is considered the reference method for glucose measurement in clinical laboratories?
- Hexokinase method (Correct answer)
- Glucose oxidase-peroxidase method
- Orthotoluidine method
- Folin-Wu reduction method
Correct answer: Hexokinase method
The hexokinase method is considered the reference method for glucose measurement due to its high specificity and accuracy.
Question 3: Which enzyme is most cardiac-specific and is considered the gold standard biomarker for myocardial infarction diagnosis?
- Creatine kinase-MB (CK-MB)
- Lactate dehydrogenase (LDH)
- Cardiac troponin I or T (Correct answer)
- Aspartate aminotransferase (AST)
Correct answer: Cardiac troponin I or T
Cardiac troponin I and T are the gold standard biomarkers for myocardial infarction due to their high cardiac specificity and sensitivity.
Question 4: The normal anion gap range is approximately 8-12 mEq/L. Which formula correctly calculates the anion gap?
- Na+ - (Cl- + HCO3-) (Correct answer)
- Na+ + K+ - (Cl- + HCO3-)
- Na+ - Cl-
- (Na+ + K+) - Cl-
Correct answer: Na+ - (Cl- + HCO3-)
The anion gap is calculated as Na+ minus the sum of Cl- and HCO3-, representing unmeasured anions in plasma.
Question 5: Which lipid fraction is inversely associated with cardiovascular disease risk and is often called 'good cholesterol'?
- LDL cholesterol
- VLDL cholesterol
- HDL cholesterol (Correct answer)
- Chylomicrons
Correct answer: HDL cholesterol
HDL cholesterol is inversely associated with cardiovascular risk because it facilitates reverse cholesterol transport from peripheral tissues to the liver.
Question 6: A serum creatinine of 2.5 mg/dL in an adult patient most likely indicates which condition?
- Normal renal function
- Impaired renal function (Correct answer)
- Hepatic failure
- Hemolytic anemia
Correct answer: Impaired renal function
A serum creatinine of 2.5 mg/dL exceeds the normal range (0.6-1.2 mg/dL) and indicates impaired glomerular filtration and renal dysfunction.
Question 7: Which of the following is the most common cause of pseudohyperkalemia in a blood specimen?
- Prolonged storage at room temperature
- Hemolysis of red blood cells in the specimen (Correct answer)
- Use of a lithium heparin tube
- Refrigeration of the specimen before centrifugation
Correct answer: Hemolysis of red blood cells in the specimen
Hemolysis releases intracellular potassium from red blood cells into the serum or plasma, causing falsely elevated potassium results.
