CLT Laboratory Equipment Operation & Maintenance 3 — Questions and Answers
Question 1: The linearity verification for a glucose analyzer should be performed using:
- Patient samples diluted in series
- Commercial linearity materials spanning the reportable range (Correct answer)
- Distilled water as a zero calibrator
- Whole blood standards only
Correct answer: Commercial linearity materials spanning the reportable range
Commercial linearity materials with certified target values spanning the analytical measurement range (AMR) are used to verify that the analyzer produces results proportional to analyte concentration across its full range.
Question 2: A pH meter requires calibration with buffers at two points before use. This is done to:
- Stabilize the electrode membrane hydration
- Compensate for temperature differences in samples
- Correct for both the offset and slope of the electrode response (Correct answer)
- Remove protein contamination from the electrode tip
Correct answer: Correct for both the offset and slope of the electrode response
Two-point calibration corrects the offset (zero intercept) and the slope of the glass electrode's response curve, ensuring accurate pH readings across the measurement range.
Question 3: When a laboratory pipette fails its gravimetric verification, the technologist should:
- Adjust the pipette's internal calibration screw and re-verify
- Return it to service at a lower volume setting
- Tag it out of service and send it for repair or recalibration (Correct answer)
- Use it only for non-critical reagent transfers
Correct answer: Tag it out of service and send it for repair or recalibration
A pipette that fails gravimetric verification must be taken out of service immediately and sent for professional recalibration or repair to prevent analytical errors.
Question 4: The function of the sheath fluid in a flow cytometer is to:
- Lyse red blood cells before analysis
- Hydrodynamically focus cells into a single-file stream (Correct answer)
- Provide nutrients to maintain cell viability
- Quench fluorescent dyes after excitation
Correct answer: Hydrodynamically focus cells into a single-file stream
Sheath fluid surrounds the sample stream in a flow cytometer, using hydrodynamic focusing to align cells single-file through the laser interrogation point for accurate individual cell analysis.
Question 5: An ion-selective electrode (ISE) analyzer for sodium shows a carryover effect between high and low samples. The MOST likely cause is:
- Insufficient washout volume between samples (Correct answer)
- Faulty reference electrode junction
- Sample clot in the specimen probe
- Incorrect calibration frequency
Correct answer: Insufficient washout volume between samples
Carryover in ISE analyzers is most commonly caused by insufficient wash volume between samples, causing residual analyte from a high sample to contaminate the next low sample.
Question 6: During preventive maintenance of an automated chemistry analyzer, the probe wash station is cleaned because:
- It sterilizes the probe between patient samples
- Protein and salt buildup can impair probe cleansing and cause carryover (Correct answer)
- It cools the probe to prevent reagent evaporation
- It is required by CLIA for every 100 patient samples
Correct answer: Protein and salt buildup can impair probe cleansing and cause carryover
Protein deposits and salt crystals accumulating in the probe wash station reduce washing effectiveness, leading to sample-to-sample carryover and inaccurate results.
Question 7: A hemocytometer is used to manually count cells. The accepted standard dilution for a WBC count using a hemocytometer is:
- 1:10 with saline
- 1:20 with acetic acid solution (Correct answer)
- 1:100 with saline
- 1:200 with saline
Correct answer: 1:20 with acetic acid solution
A 1:20 dilution with 3% acetic acid (Türk's solution) is the standard for manual WBC hemocytometer counts — the acid lyses RBCs while preserving WBCs for counting.
CLT Laboratory Equipment Operation & Maintenance 3
The linearity verification for a glucose analyzer should be performed using: