CMLA Laboratory Equipment Operation & Maintenance 5 — Questions and Answers
Question 1: Which action protects pipette accuracy when aspirating volatile reagents such as acetone?
- Increase aspiration speed
- Pre-wet the pipette tip with the reagent before aspirating the target volume (Correct answer)
- Dispense the reagent slowly into an open container
- Use a glass pipette only
Correct answer: Pre-wet the pipette tip with the reagent before aspirating the target volume
Pre-wetting saturates the dead air space inside the tip, reducing evaporation and improving volume accuracy for volatile liquids.
Question 2: How often should the HEPA filter in a Class II Type A2 biological safety cabinet typically be certified?
- Monthly
- Annually or whenever the cabinet is moved or serviced (Correct answer)
- Every 5 years
- Only when the unit fails a visual inspection
Correct answer: Annually or whenever the cabinet is moved or serviced
NSF/ANSI 49 requires annual certification of BSCs, plus recertification after relocation or major service, to verify airflow and HEPA filter integrity.
Question 3: What does the term 'carry-over' mean in the context of automated laboratory analyzers?
- The volume of specimen left in the tube after testing
- Residual analyte from a previous sample contaminating the next sample result (Correct answer)
- Transport of specimens from one department to another
- Transfer of QC data between analyzer runs
Correct answer: Residual analyte from a previous sample contaminating the next sample result
Carry-over occurs when residual analyte from a high-concentration sample contaminates the subsequent sample, falsely elevating or affecting that result.
Question 4: A freezer storing frozen plasma is found at –15°C instead of the required ≤–20°C. What is the primary concern?
- The freezer door may have been left open briefly
- Labile coagulation factors in the plasma may have degraded (Correct answer)
- The thermometer is likely malfunctioning
- The freezer motor is too powerful
Correct answer: Labile coagulation factors in the plasma may have degraded
Temperatures above –20°C accelerate degradation of labile coagulation factors such as Factor V and Factor VIII in frozen plasma.
Question 5: Why should a centrifuge rotor be inspected for cracks or corrosion before each use?
- Cracks improve rotor balance
- A compromised rotor can fail catastrophically at high speed, causing injury (Correct answer)
- Corrosion increases rotor speed
- Visual inspection is required only annually
Correct answer: A compromised rotor can fail catastrophically at high speed, causing injury
Cracks or corrosion weaken the rotor structure and can lead to explosive rotor failure under centrifugal force, posing serious risk to laboratory personnel.
Question 6: When changing a reagent lot on a chemistry analyzer, which step must be completed before reporting patient results?
- Notify the supervisor only
- Run quality control with the new lot and verify results are within acceptable ranges (Correct answer)
- Adjust all patient results by 5%
- Perform only a visual reagent inspection
Correct answer: Run quality control with the new lot and verify results are within acceptable ranges
QC must pass with the new reagent lot before patient testing resumes, ensuring the new reagents perform acceptably.
Question 7: Which of the following best describes the purpose of an internal standard in an automated analyzer?
- A reagent added to prevent microbial growth
- A known-concentration substance added to correct for sample-to-sample variation in signal (Correct answer)
- A QC material run between patient samples
- A calibration curve stored in analyzer memory
Correct answer: A known-concentration substance added to correct for sample-to-sample variation in signal
Internal standards compensate for matrix effects and instrument variation by normalizing analyte signal to the known signal of the internal standard in each sample.
CMLA Laboratory Equipment Operation & Maintenance 5
Which action protects pipette accuracy when aspirating volatile reagents such as acetone?