CMLA Quality Control & Assurance in Laboratory Practices 3 — Questions and Answers
Question 1: A laboratory assistant notices the QC mean has gradually increased over 30 days. What is the most likely cause?
- Random pipetting errors
- Reagent deterioration or calibration drift (Correct answer)
- Improper sample collection
- Clerical transcription errors
Correct answer: Reagent deterioration or calibration drift
A gradual shift in the QC mean over time typically indicates reagent deterioration, instrument drift, or a calibration issue requiring investigation.
Question 2: What action should be taken when proficiency testing results are found to be unacceptable?
- Discard the results and reorder the PT samples
- Document and submit a corrective action plan to the accrediting body (Correct answer)
- Report only the passing analytes to the accreditor
- Wait for the next PT cycle to assess performance
Correct answer: Document and submit a corrective action plan to the accrediting body
Unacceptable PT results require documentation, root cause analysis, and a corrective action plan submitted to the accrediting organization.
Question 3: Which of the following best describes the difference between accuracy and precision in laboratory QC?
- Accuracy measures reproducibility; precision measures closeness to true value
- Accuracy measures closeness to true value; precision measures reproducibility (Correct answer)
- Both terms describe the same concept in clinical laboratories
- Accuracy applies to calibrators; precision applies to controls
Correct answer: Accuracy measures closeness to true value; precision measures reproducibility
Accuracy refers to how close a result is to the true value, while precision refers to how reproducible repeated measurements are.
Question 4: A calibration verification requires testing patient-like samples at a minimum of how many concentration levels?
- Two levels (low and high)
- Three levels (low, mid, high) (Correct answer)
- Five levels across the full range
- One level at the medical decision point
Correct answer: Three levels (low, mid, high)
CLIA requires calibration verification at a minimum of three levels (low, mid, and high) spanning the reportable range.
Question 5: Which QC approach involves using patient data statistics such as the average of normals (AON) to monitor analytical performance?
- Westgard multirule approach
- Patient-based real-time QC (PBRTQC) (Correct answer)
- Levy-Jennings charting
- Delta check method
Correct answer: Patient-based real-time QC (PBRTQC)
Patient-based real-time QC uses the statistical distribution of patient results to detect systematic errors without relying solely on traditional controls.
Question 6: When a new reagent lot is placed into service, the laboratory should first:
- Run patient samples immediately to confirm performance
- Perform parallel testing with the old and new lot before switching (Correct answer)
- Dispose of all remaining old-lot reagents
- Contact the manufacturer for new control ranges
Correct answer: Perform parallel testing with the old and new lot before switching
Parallel testing of old and new reagent lots ensures equivalent performance before transitioning to the new lot to protect patient safety.
Question 7: The R-4s Westgard rule is triggered when:
- One control exceeds ±4 standard deviations from the mean
- The range between two controls within the same run exceeds 4 standard deviations (Correct answer)
- Four consecutive controls exceed ±1 standard deviation
- Two controls in separate runs both exceed ±2 standard deviations
Correct answer: The range between two controls within the same run exceeds 4 standard deviations
The R-4s rule flags a run when the difference between the highest and lowest control values within one run is greater than 4 standard deviations, indicating random error.
CMLA Quality Control & Assurance in Laboratory Practices 3
A laboratory assistant notices the QC mean has gradually increased over 30 days.
What is the most likely cause?