SCYM Quality Control & Assurance 3 — Questions and Answers
Question 1: In cytometry, 'carryover' contamination between samples is best minimized by:
- Running a wash or rinse cycle between samples (Correct answer)
- Increasing the flow rate for every sample
- Applying a higher gain setting on all detectors
- Using a different laser for each sample
Correct answer: Running a wash or rinse cycle between samples
Wash or rinse cycles flush residual cells from the fluidics pathway, preventing carry-over to the next sample.
Question 2: What defines the linear dynamic range of a flow cytometer detector?
- The range of signal intensities over which detector response is proportional to fluorescence input (Correct answer)
- The spread of emission spectra across all channels
- The maximum number of events that can be acquired per second
- The sensitivity threshold below which no events are recorded
Correct answer: The range of signal intensities over which detector response is proportional to fluorescence input
Linear dynamic range is the span of intensities where the detector produces a proportional, accurate output without saturation.
Question 3: A lab processes QC samples at the beginning and end of each analytical run. This practice is designed to detect:
- Instrument drift occurring during the run (Correct answer)
- Reagent lot-to-lot variability
- Operator-to-operator variability only
- Sample storage degradation
Correct answer: Instrument drift occurring during the run
Bracketing runs with QC samples reveals drift in instrument performance across the analytical session.
Question 4: Which action should be taken when a QC result fails the Westgard 1-3s warning rule?
- Investigate potential causes and perform additional QC testing before releasing patient results (Correct answer)
- Immediately recalibrate all PMTs and re-run all patient samples from that day
- Report patient results with a notation of borderline QC
- Discard the QC material and open a new vial
Correct answer: Investigate potential causes and perform additional QC testing before releasing patient results
The 1-3s exceedance is a warning signal; laboratory protocol requires investigation and confirmatory QC before patient results are released.
Question 5: Light scatter QC on a flow cytometer typically uses which type of reference material?
- Polystyrene microspheres of defined size (Correct answer)
- Fluorescent antibody-labeled peripheral blood
- Calibrated fluorescent dye solutions
- Unstained whole blood cells only
Correct answer: Polystyrene microspheres of defined size
Polystyrene microspheres have defined, stable size and refractive index, making them ideal for light scatter alignment and QC.
Question 6: Which document type formally records the acceptable performance specifications for a clinical cytometry assay?
- Standard operating procedure (SOP) (Correct answer)
- Material Safety Data Sheet (MSDS)
- Certificate of Analysis (CoA)
- Instrument service log
Correct answer: Standard operating procedure (SOP)
SOPs define the acceptable performance criteria, methods, and corrective actions for clinical cytometry assays.
Question 7: When establishing QC ranges for a new lot of cytometry beads, the recommended minimum number of data points collected over multiple days is:
- At least 20 data points across ≥5 days (Correct answer)
- 3 data points from a single run
- 10 data points from a single day
- 50 data points from one operator
Correct answer: At least 20 data points across ≥5 days
CLSI and CAP guidelines recommend ≥20 data points collected over multiple days to capture within- and between-day variability when setting QC ranges.
SCYM Quality Control & Assurance 3
In cytometry, 'carryover' contamination between samples is best minimized by: