MLPAO Clinical Chemistry Advanced Concepts 1 — Questions and Answers
Question 1: Which method is used as the reference standard for measuring serum cholesterol?
- Enzymatic cholesterol oxidase method
- Abell-Kendall method (Correct answer)
- Liebermann-Burchard method
- Gas chromatography-mass spectrometry
Correct answer: Abell-Kendall method
The Abell-Kendall method is the CDC reference method for total cholesterol measurement. It involves saponification, extraction with petroleum ether, and colorimetric measurement using the Liebermann-Burchard reaction. Routine clinical laboratories typically use enzymatic methods calibrated against this reference.
Question 2: What is the Friedewald equation used to calculate?
- HDL cholesterol
- LDL cholesterol (Correct answer)
- VLDL cholesterol
- Total cholesterol
Correct answer: LDL cholesterol
The Friedewald equation estimates LDL cholesterol: LDL = Total Cholesterol - HDL - (Triglycerides/2.2) in mmol/L. This equation is unreliable when triglycerides exceed 4.5 mmol/L or when chylomicrons are present, requiring direct LDL measurement instead.
Question 3: Which analyte requires collection in a tube containing sodium fluoride to prevent glycolysis?
- Potassium
- Glucose (Correct answer)
- Calcium
- Bilirubin
Correct answer: Glucose
Glucose specimens require sodium fluoride (grey-top tube) to inhibit glycolysis by red blood cells and white blood cells. Without this preservative, glucose decreases approximately 5-7% per hour at room temperature due to continued cellular metabolism.
Question 4: What is the principle behind the enzymatic method for measuring serum triglycerides?
- Direct spectrophotometric absorption of triglycerides
- Lipase hydrolysis followed by glycerol kinase reaction (Correct answer)
- Saponification with potassium hydroxide
- Thin-layer chromatography separation
Correct answer: Lipase hydrolysis followed by glycerol kinase reaction
The enzymatic method for triglycerides involves lipase hydrolysis to release glycerol, which is then phosphorylated by glycerol kinase. Subsequent enzymatic reactions produce a colored compound or hydrogen peroxide that is measured spectrophotometrically.
Question 5: In therapeutic drug monitoring (TDM), what is a 'trough' level?
- The maximum drug concentration after a dose
- The minimum drug concentration just before the next dose (Correct answer)
- The average drug concentration over a dosing interval
- The drug concentration at steady state
Correct answer: The minimum drug concentration just before the next dose
A trough level is the lowest concentration of a drug in the blood, typically measured just before the next scheduled dose. Trough levels are important for drugs with narrow therapeutic indices to ensure the drug remains above the minimum effective concentration while avoiding toxicity.
Question 6: Which condition is associated with elevated serum uric acid levels?
- Hypothyroidism
- Gout (Correct answer)
- Iron deficiency anemia
- Addison disease
Correct answer: Gout
Elevated serum uric acid (hyperuricemia) is the hallmark biochemical finding in gout. Uric acid is the end product of purine metabolism, and when levels exceed solubility limits, monosodium urate crystals deposit in joints causing acute inflammatory arthritis.
MLPAO Clinical Chemistry Advanced Concepts 1
Which method is used as the reference standard for measuring serum cholesterol?