ISAC Quality Control and Assurance 2 — Questions and Answers
Question 1: Which Levey-Jennings rule flags a run as out of control when two consecutive measurements fall more than 2 standard deviations from the mean on the same side?
- 1₂s rule
- 2₂s rule (Correct answer)
- R₄s rule
- 4₁s rule
Correct answer: 2₂s rule
The 2₂s rule is violated when two consecutive control values exceed the same ±2 SD limit, indicating a systematic shift.
Question 2: In flow cytometry, the coefficient of variation (CV) of a fluorescent bead peak is used primarily to assess which instrument performance characteristic?
- Detector linearity
- Laser power stability
- Resolution or precision of measurement (Correct answer)
- Scatter signal sensitivity
Correct answer: Resolution or precision of measurement
A narrow CV on a bead peak reflects tight instrument precision; a rising CV indicates degraded resolution.
Question 3: A laboratory notices that its CD4 count results are consistently 10% higher than the previous week's values using the same reagent lot. The most likely cause is:
- Random pipetting error
- A systematic instrument or calibration shift (Correct answer)
- Patient sample degradation
- Random reagent variation
Correct answer: A systematic instrument or calibration shift
A consistent directional bias over time is characteristic of a systematic error such as a calibration or instrument drift.
Question 4: What is the primary purpose of running a process control chart in a clinical flow cytometry lab?
- To track patient demographics over time
- To monitor assay stability and detect shifts or trends before they affect patient results (Correct answer)
- To compare results between different institutions
- To record reagent expiration dates
Correct answer: To monitor assay stability and detect shifts or trends before they affect patient results
Process control charts provide ongoing visual monitoring of assay performance to catch drift or shifts early.
Question 5: Which of the following best describes the purpose of a linearity study in flow cytometry instrument qualification?
- Confirming that laser wavelengths are correctly assigned
- Verifying that the instrument produces proportional signal output across a range of input intensities (Correct answer)
- Measuring the temperature stability of the instrument
- Checking that scatter parameters are properly gated
Correct answer: Verifying that the instrument produces proportional signal output across a range of input intensities
Linearity studies confirm that the detector response is proportional to fluorescence intensity across the dynamic range.
Question 6: When establishing reference ranges for a new flow cytometry panel in a clinical lab, the minimum number of healthy donors recommended by CLSI guidelines is:
- 10
- 20
- 120 (Correct answer)
- 200
Correct answer: 120
CLSI EP28-A3c recommends a minimum of 120 reference individuals to establish robust reference intervals.
Question 7: In cytometry, 'carryover' contamination between samples is best detected by:
- Running a blank water sample after a high-count specimen and measuring residual events (Correct answer)
- Checking the CV of control beads
- Reviewing scatter plots for doublets
- Monitoring laser power fluctuations
Correct answer: Running a blank water sample after a high-count specimen and measuring residual events
Carryover is quantified by running a negative or blank sample immediately after a high-concentration specimen and counting residual events.
ISAC Quality Control and Assurance 2
Which Levey-Jennings rule flags a run as out of control when two consecutive measurements fall more than 2 standard deviations from the mean on the same side?