CMT Clinical Chemistry 5 — Questions and Answers
Question 1: Two consecutive control results exceed +2 SD on the same side of the mean. This violates which Westgard rule, and what error does it indicate?
- R-4s; random error
- 2-2s; systematic error (Correct answer)
- 10x; random error
- 1-3s; random error
Correct answer: 2-2s; systematic error
2-2s rejects a run when two consecutive controls exceed 2 SD on the same side, which signals systematic bias.
Question 2: According to Beer's law, absorbance is:
- Independent of path length
- Inversely proportional to concentration
- Logarithmically related to concentration
- Directly proportional to concentration (Correct answer)
Correct answer: Directly proportional to concentration
A = abc, so absorbance increases linearly with concentration at a fixed path length.
Question 3: The Jaffe method for creatinine uses which reagent?
- Biuret reagent
- Alkaline picrate (Correct answer)
- Bromcresol green
- Diacetyl monoxime
Correct answer: Alkaline picrate
Creatinine reacts with picrate in alkaline solution to form a red-orange complex.
Question 4: Increased conjugated bilirubin, positive urine bilirubin, and decreased urine urobilinogen most strongly suggest:
- Gilbert syndrome
- Biliary obstruction (Correct answer)
- Hemolytic anemia
- Neonatal physiologic jaundice
Correct answer: Biliary obstruction
Blockage stops bilirubin reaching the gut, so urobilinogen falls while water-soluble conjugated bilirubin spills into urine.
Question 5: Which handling requirement is most critical for a serum bilirubin specimen?
- Collect on ice
- Keep at 37°C
- Collect in a fluoride tube
- Protect from light (Correct answer)
Correct answer: Protect from light
Light breaks down bilirubin and causes falsely low results.
Question 6: For a plasma ammonia level, the specimen should be:
- Placed on ice and analyzed promptly (Correct answer)
- Allowed to clot at room temperature for 1 hour
- Stored at room temperature overnight
- Collected from a tight, prolonged tourniquet
Correct answer: Placed on ice and analyzed promptly
Red cell metabolism and deamination in vitro raise ammonia quickly, so chilling and fast testing are essential.
Question 7: Urine creatinine 100 mg/dL, plasma creatinine 1.0 mg/dL, 24-hour urine volume 1440 mL. What is the creatinine clearance?
- 100 mL/min (Correct answer)
- 144 mL/min
- 72 mL/min
- 1440 mL/min
Correct answer: 100 mL/min
1440 mL/day is 1 mL/min, so clearance = (100 × 1)/1.0 = 100 mL/min.
CMT Clinical Chemistry 5
Two consecutive control results exceed +2 SD on the same side of the mean.
This violates which Westgard rule, and what error does it indicate?