CLIA Testing Procedures & Method Validation 4 — Questions and Answers
Question 1: A technologist performing a glucose assay obtains QC results of 98 mg/dL and 102 mg/dL for a control with a mean of 100 mg/dL and SD of 3 mg/dL. Which Westgard rule applies?
- 1₂s warning
- 1₃s rejection
- 2₂s rejection
- Within acceptable limits — no rule violated (Correct answer)
Correct answer: Within acceptable limits — no rule violated
Both values fall within ±2 SD of the mean (±6 mg/dL), so no Westgard warning or rejection rule is triggered.
Question 2: What is 'carryover' in the context of analytical testing, and why is it evaluated during method validation?
- The transfer of analyte from a high-concentration sample to a subsequent low-concentration sample, potentially causing falsely elevated results (Correct answer)
- The degradation of reagent over time due to temperature changes
- The systematic difference between two analytical methods
- Variation in results caused by different operators
Correct answer: The transfer of analyte from a high-concentration sample to a subsequent low-concentration sample, potentially causing falsely elevated results
Carryover occurs when residual analyte from a previous high-concentration sample contaminates the next sample, and it must be evaluated to prevent false results.
Question 3: Which parameter best describes a method's ability to detect small differences in analyte concentration between two samples?
- Analytical sensitivity (Correct answer)
- Analytical specificity
- Linearity
- Reportable range
Correct answer: Analytical sensitivity
Analytical sensitivity refers to the ability of a method to detect small changes in analyte concentration, often expressed as the slope of the calibration curve.
Question 4: When validating a laboratory-developed test (LDT) for a high-complexity analyte, which performance characteristic is NOT required by CLIA to be established?
- Accuracy
- Precision
- Reportable range
- Cost per test (Correct answer)
Correct answer: Cost per test
CLIA mandates validation of accuracy, precision, reportable range, reference intervals, and interferences, but cost per test is a business consideration, not a regulatory requirement.
Question 5: A laboratory is validating a new serum creatinine method. Specimens with creatinine >10 mg/dL are routinely diluted 1:5. The laboratory must verify that:
- The dilution protocol does not alter the matrix significantly and diluted results are accurate (Correct answer)
- Dilution is only performed for QC samples, not patient samples
- The lowest reportable value is ≤0.1 mg/dL
- The method's CV is <5% at all dilutions
Correct answer: The dilution protocol does not alter the matrix significantly and diluted results are accurate
When dilution extends the reportable range, the laboratory must verify that the dilution protocol maintains accuracy and does not introduce matrix-dependent errors.
Question 6: Which statistical test is most appropriate for comparing bias between a new method and a comparative (reference) method in a method comparison study?
- Chi-square test
- Paired t-test or Deming regression (Correct answer)
- ANOVA
- Fisher's exact test
Correct answer: Paired t-test or Deming regression
Paired t-tests assess average bias between methods, and Deming (or Passing-Bablok) regression accounts for error in both methods during comparison.
Question 7: According to CLIA, for non-waived tests, how long must a laboratory retain records of quality control results?
- 6 months
- 1 year
- 2 years (Correct answer)
- 5 years
Correct answer: 2 years
CLIA requires non-waived laboratories to retain QC records for a minimum of 2 years.
CLIA Testing Procedures & Method Validation 4
A technologist performing a glucose assay obtains QC results of 98 mg/dL and 102 mg/dL for a control with a mean of 100 mg/dL and SD of 3 mg/dL.
Which Westgard rule applies?