SCYM Quality Control & Assurance 4 — Questions and Answers
Question 1: A spectral overlap correction matrix is recalculated after changing which of the following?
- Fluorochrome-conjugated antibodies or fluorochromes used in the panel (Correct answer)
- The number of events acquired per sample
- The sample acquisition flow rate
- The threshold for debris exclusion
Correct answer: Fluorochrome-conjugated antibodies or fluorochromes used in the panel
Compensation matrices are specific to the fluorochromes in use; changing any dye requires recalculating spillover to maintain accuracy.
Question 2: In clinical cytometry, proficiency testing (PT) programs serve primarily to:
- Evaluate laboratory performance by comparing results to peer laboratories and reference values (Correct answer)
- Replace internal QC for regulated analytes
- Determine instrument maintenance schedules
- Standardize antibody clone selection across all labs
Correct answer: Evaluate laboratory performance by comparing results to peer laboratories and reference values
PT programs assess inter-laboratory performance by distributing the same challenge samples to multiple labs and comparing results.
Question 3: Which of the following best describes 'assay sensitivity' in the context of flow cytometry QC?
- The lowest concentration of the analyte the assay can reliably detect (Correct answer)
- The percentage of true negatives correctly identified
- The reproducibility of replicate measurements
- The ratio of signal to background noise of the detector
Correct answer: The lowest concentration of the analyte the assay can reliably detect
Assay sensitivity (limit of detection or LoD) is the minimum analyte level that can be distinguished from background with statistical confidence.
Question 4: A laboratory wants to verify that its CD4 T-cell count assay meets clinical decision thresholds. Which validation study is most appropriate?
- Linearity and reportable range study across clinically relevant concentrations (Correct answer)
- Antibody titration optimization study
- Fluorochrome quantum yield comparison
- Panel building using spectral unmixing software
Correct answer: Linearity and reportable range study across clinically relevant concentrations
Linearity studies confirm that the assay produces accurate results across the full reportable range needed for clinical decisions.
Question 5: CAP accreditation for clinical flow cytometry laboratories requires participation in proficiency testing how often?
- Typically three times per year for regulated analytes (Correct answer)
- Once per year for all analytes
- Monthly for all analytes
- Only upon initial accreditation
Correct answer: Typically three times per year for regulated analytes
CAP generally mandates three PT challenges per year for regulated clinical flow cytometry analytes.
Question 6: Which of the following is a key requirement for a corrective action report after a QC failure in a CLIA-regulated laboratory?
- Documentation of the root cause, action taken, and verification that the corrective action resolved the issue (Correct answer)
- Verbal notification to the laboratory director only
- Immediate disposal of all samples from the failed run
- Recalibration of the instrument without further documentation
Correct answer: Documentation of the root cause, action taken, and verification that the corrective action resolved the issue
CLIA mandates written documentation of root cause analysis, corrective action, and verification of resolution for all QC failures.
Question 7: When validating a multicolor flow cytometry panel for clinical use, 'specificity' is assessed by:
- Testing the panel against samples known to be negative for the target population and confirming absence of false positives (Correct answer)
- Measuring the fluorescence intensity of the brightest staining antibody
- Comparing event counts to a hemocytometer count
- Running the panel on a single normal donor sample
Correct answer: Testing the panel against samples known to be negative for the target population and confirming absence of false positives
Specificity validation requires confirmed-negative samples to ensure the assay does not erroneously identify non-target cells as positive.
SCYM Quality Control & Assurance 4
A spectral overlap correction matrix is recalculated after changing which of the following?