CLT Clinical Laboratory Techniques & Procedures 2 — Questions and Answers
Question 1: Which centrifuge speed is most appropriate for separating serum from a whole blood specimen?
- 1,000–2,000 rpm for 5 minutes
- 2,000–3,000 rpm for 10 minutes (Correct answer)
- 5,000–10,000 rpm for 15 minutes
- 15,000–20,000 rpm for 5 minutes
Correct answer: 2,000–3,000 rpm for 10 minutes
Routine serum separation requires centrifugation at approximately 2,000–3,000 rpm for 10 minutes to pellet cells without hemolysis.
Question 2: A laboratory technologist notices a clot in an EDTA tube collected for a CBC. What is the most appropriate action?
- Run the sample and note the clot in comments
- Recollect the specimen from the patient (Correct answer)
- Dilute the sample with saline to dissolve the clot
- Vortex the tube vigorously to break up the clot
Correct answer: Recollect the specimen from the patient
Clotted EDTA specimens are unsuitable for CBC analysis and must be recollected because platelet counts and cell morphology will be inaccurate.
Question 3: The delta check system in laboratory information systems is primarily used to:
- Flag specimens with lipemia or icterus
- Compare a current result with a previous result from the same patient (Correct answer)
- Alert staff to reagent lot number changes
- Monitor QC chart Westgard rule violations
Correct answer: Compare a current result with a previous result from the same patient
Delta checks compare current patient results against prior results to detect specimen mix-ups, labeling errors, or unexpected clinical changes.
Question 4: When performing a manual differential on a peripheral blood smear, the technologist should count how many cells?
- 50 WBCs
- 100 WBCs (Correct answer)
- 200 WBCs
- 500 WBCs
Correct answer: 100 WBCs
The standard manual differential requires counting 100 WBCs in the monolayer area of the smear to classify cell types as percentages.
Question 5: Which specimen type is required for a plasma renin activity (PRA) test?
- Serum (red-top tube)
- EDTA plasma (lavender-top tube) (Correct answer)
- Citrate plasma (blue-top tube)
- Heparin plasma (green-top tube)
Correct answer: EDTA plasma (lavender-top tube)
PRA requires EDTA plasma collected on ice because EDTA chelates calcium to inhibit angiotensin-converting enzyme and the cold slows enzymatic degradation.
Question 6: A 2% sodium hypochlorite (bleach) solution is used in the clinical laboratory primarily as a:
- Fixative for tissue specimens
- High-level disinfectant for critical instruments
- Surface decontaminant for blood spills (Correct answer)
- Preservative for urine cultures
Correct answer: Surface decontaminant for blood spills
A 1:10 dilution of household bleach (≈0.5%) or 1:5 dilution (≈1%) is the standard decontaminant for blood and body-fluid spills on bench surfaces.
Question 7: Which of the following best describes the purpose of an internal standard in quantitative mass spectrometry assays?
- It calibrates the instrument's ion source voltage
- It corrects for matrix effects and variability in extraction efficiency (Correct answer)
- It acts as a positive quality control sample
- It sets the upper limit of the reportable range
Correct answer: It corrects for matrix effects and variability in extraction efficiency
An isotope-labeled internal standard co-elutes with the analyte and compensates for ion suppression, extraction losses, and injection-to-injection variability.
CLT Clinical Laboratory Techniques & Procedures 2
Which centrifuge speed is most appropriate for separating serum from a whole blood specimen?