MLPAO Clinical Chemistry Laboratory Practice

Question 1

What is the purpose of a reagent blank in spectrophotometric clinical chemistry assays?

Accepted Answer

To correct for absorbance contributed by reagents and cuvette rather than the analyte

Answer

A reagent blank measures the absorbance of all components except the analyte of interest (reagents, diluent, cuvette). This value is subtracted from the sample reading to ensure that only the absorbance due to the analyte is measured, improving accuracy.

Question 2

Which analyte is most affected by improper specimen transport temperature?

Accepted Answer

Ammonia

Answer

Ammonia is extremely sensitive to transport conditions. Specimens must be placed on ice immediately after collection and analyzed within 15-30 minutes. At room temperature, deamination of amino acids and other nitrogen-containing compounds causes rapid ammonia generation, leading to falsely elevated results.

Question 3

What is the clinical significance of measuring cystatin C?

Accepted Answer

Estimating GFR independent of muscle mass

Answer

Cystatin C is a small protein produced at a constant rate by all nucleated cells and freely filtered by the glomerulus. Unlike creatinine, cystatin C is not significantly affected by muscle mass, age, or sex, making it a more reliable GFR marker in patients with extremes of body composition.

Question 4

Which Westgard rule is considered a 'warning' rule rather than a rejection rule?

Accepted Answer

1-2s

Answer

The 1-2s rule is a warning rule that triggers inspection of additional QC data. A single QC result exceeding 2 standard deviations from the mean occurs randomly about 5% of the time and does not alone indicate an analytical problem. It prompts checking other Westgard rules for true violations.

Question 5

What is Beer's Law and how does it apply to clinical chemistry?

Accepted Answer

It states that absorbance is directly proportional to the concentration of the absorbing substance and path length

Answer

Beer's Law (A = εbc) states that absorbance is directly proportional to the molar absorptivity (ε), path length (b), and concentration (c) of the absorbing substance. This is the fundamental principle underlying spectrophotometric measurements in clinical chemistry, allowing concentration to be determined from absorbance readings.

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO Clinical Chemistry Laboratory Practice