CLT Clinical Laboratory Techniques & Procedures 3 — Questions and Answers
Question 1: Which quality control rule indicates a systematic error when two consecutive QC results fall more than 2 standard deviations in the same direction?
- 1-2s warning rule
- 2-2s rule (Correct answer)
- R-4s rule
- 10-x rule
Correct answer: 2-2s rule
The 2-2s Westgard rule is triggered when two consecutive QC values exceed 2 SD on the same side of the mean, indicating systematic bias.
Question 2: A urine specific gravity of 1.035 measured by refractometry would be best described as:
- Isosthenuric
- Hyposthenuric
- Hypersthenuric (Correct answer)
- Glucosuric artifact
Correct answer: Hypersthenuric
Hypersthenuria refers to urine with a specific gravity above 1.030, indicating highly concentrated urine, which can occur in dehydration or ADH excess.
Question 3: When calibrating a micropipette for accuracy verification, the preferred method is:
- Timing how long it takes to aspirate a fixed volume
- Gravimetric measurement of dispensed distilled water (Correct answer)
- Comparing results with a neighboring pipette
- Using a turbidimetric standard solution
Correct answer: Gravimetric measurement of dispensed distilled water
Gravimetric verification weighs the dispensed water on an analytical balance; using the density of water at a known temperature converts mass to volume.
Question 4: Which of the following is the primary reason for using a silica gel desiccant in reagent strip storage containers?
- To prevent microbial growth on the strips
- To maintain strip performance by absorbing moisture (Correct answer)
- To keep the strips from reacting with light
- To neutralize acidic vapors from urine
Correct answer: To maintain strip performance by absorbing moisture
Moisture degrades the chemical reagent pads on urinalysis strips; the desiccant absorbs ambient humidity to extend shelf life and preserve reactivity.
Question 5: A technologist is performing an acid-fast stain (Ziehl-Neelsen). What is the role of the carbol fuchsin heating step?
- It kills mycobacteria so they are safe to handle
- It drives the dye into the waxy mycobacterial cell wall (Correct answer)
- It decolorizes non-acid-fast organisms
- It enhances Gram-positive cell wall staining
Correct answer: It drives the dye into the waxy mycobacterial cell wall
Heat facilitates penetration of carbol fuchsin through the high-lipid mycobacterial cell wall; the dye is then retained after acid-alcohol decolorization.
Question 6: When preparing a blood smear for a malaria parasite examination, the thick smear differs from the thin smear in that it:
- Is stained with Gram stain instead of Giemsa
- Uses lysed red cells to concentrate parasites for detection (Correct answer)
- Allows precise species identification due to preserved cell morphology
- Requires immediate fixation with methanol before staining
Correct answer: Uses lysed red cells to concentrate parasites for detection
Thick smears lyse RBCs during staining, concentrating parasites for higher sensitivity, but RBC morphology is lost, making species ID difficult.
Question 7: A linear regression QC study comparing a new analyzer to a reference method yields a slope of 1.08 and an intercept of -2.5 mg/dL. This result indicates:
- Good agreement; both slope and intercept are clinically acceptable
- Proportional error only, with no constant bias
- Constant error only, with no proportional bias
- Both proportional and constant errors are present (Correct answer)
Correct answer: Both proportional and constant errors are present
A slope ≠ 1.00 indicates proportional error, while an intercept ≠ 0 indicates constant error; both are present in this case.
CLT Clinical Laboratory Techniques & Procedures 3
Which quality control rule indicates a systematic error when two consecutive QC results fall more than 2 standard deviations in the same direction?