MLPAO Clinical Chemistry Advanced Concepts

Question 1

Which method is used as the reference standard for measuring serum cholesterol?

Accepted Answer

Abell-Kendall method

Answer

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?

Accepted Answer

LDL cholesterol

Answer

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?

Accepted Answer

Glucose

Answer

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?

Accepted Answer

Lipase hydrolysis followed by glycerol kinase reaction

Answer

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?

Accepted Answer

The minimum drug concentration just before the next dose

Answer

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.

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO Clinical Chemistry Advanced Concepts