SCYM Quality Control & Assurance 2 — Questions and Answers
Question 1: Which metric is used to assess the day-to-day reproducibility of a flow cytometer's fluorescence measurements?
- Coefficient of variation (CV) of bead populations (Correct answer)
- Mean fluorescence intensity of unstained cells
- Forward scatter area of lymphocytes
- Spectral overlap correction factor
Correct answer: Coefficient of variation (CV) of bead populations
CV of fluorescent bead populations measured daily quantifies instrument reproducibility and flags instrument drift.
Question 2: A lab notices that the CV for their daily QC beads has increased from 2% to 6% over one week. The most likely cause is:
- Laser power instability or a failing detector (Correct answer)
- Incorrect gating strategy applied to beads
- Improper compensation settings
- Sample carryover from the previous run
Correct answer: Laser power instability or a failing detector
Widening bead CVs typically indicate laser instability, detector degradation, or optical misalignment.
Question 3: What is the purpose of running an unstained control in cytometry QC?
- To establish the autofluorescence baseline of the cell population (Correct answer)
- To calibrate the laser power output
- To determine antibody titration curves
- To measure spectral spillover values
Correct answer: To establish the autofluorescence baseline of the cell population
Unstained controls define the autofluorescence level, enabling proper gating of negative populations.
Question 4: Which of the following best describes the role of a fluorescence-minus-one (FMO) control?
- It identifies the spread of fluorescence into a channel of interest from all other fluorochromes except one (Correct answer)
- It corrects for instrument noise in each detector
- It measures non-specific antibody binding
- It establishes the gate for debris exclusion
Correct answer: It identifies the spread of fluorescence into a channel of interest from all other fluorochromes except one
FMO controls capture spillover spread from all other channels into the channel of interest, defining the true negative boundary.
Question 5: A flow cytometry lab implements Levey-Jennings charts for QC bead data. A data point falling 3 standard deviations from the mean indicates:
- An out-of-control condition requiring investigation before patient samples are reported (Correct answer)
- Normal biological variation acceptable for release
- A need to recalibrate antibody panels only
- That compensation must be re-applied
Correct answer: An out-of-control condition requiring investigation before patient samples are reported
Per Westgard rules, a 3SD exceedance is an out-of-control signal mandating investigation and corrective action.
Question 6: When validating a new cytometer for clinical use, which parameter is specifically assessed by running the same sample on both the new and reference instrument?
- Method correlation and bias (Correct answer)
- Fluorochrome quantum yield
- Detector quantum efficiency
- Laser wavelength accuracy
Correct answer: Method correlation and bias
Method correlation studies compare results between instruments to assess bias and ensure clinical equivalence.
Question 7: Which Westgard rule is violated when two consecutive QC measurements both exceed the same 2SD limit in the same direction?
- 2-2s rule (Correct answer)
- 1-3s rule
- R-4s rule
- 4-1s rule
Correct answer: 2-2s rule
The 2-2s rule is triggered when two consecutive control values exceed +2SD or both fall below -2SD, indicating systematic error.
SCYM Quality Control & Assurance 2
Which metric is used to assess the day-to-day reproducibility of a flow cytometer's fluorescence measurements?