SCYM Compensation Techniques 2 ā Questions and Answers
Question 1: In multicolor flow cytometry, what is the consequence of under-compensation for spectral spillover?
- False-positive signal appears in the spillover channel (Correct answer)
- False-negative signal appears in the spillover channel
- The primary detector channel shows decreased MFI
- Scatter parameters are distorted
Correct answer: False-positive signal appears in the spillover channel
Under-compensation leaves residual donor signal in the acceptor channel, creating a false-positive shift.
Question 2: Which mathematical relationship defines the spillover coefficient used in compensation matrices?
- Ratio of signal in off-target channel to signal in primary channel for a single-stained control (Correct answer)
- Ratio of primary channel MFI to unstained MFI
- Difference between positive and negative population medians
- Product of detector QE and filter bandwidth
Correct answer: Ratio of signal in off-target channel to signal in primary channel for a single-stained control
The spillover coefficient is calculated as the off-target channel signal divided by the primary channel signal from a single-color control.
Question 3: When using AutoMACS beads for compensation controls, what is the critical requirement for accuracy?
- Beads must be stained with the same lot of antibody used in the experiment
- Bead signal must be at least as bright as the brightest cell population (Correct answer)
- Beads must be run at the same flow rate as experimental samples
- Beads must be fixed before acquisition
Correct answer: Bead signal must be at least as bright as the brightest cell population
Compensation beads must generate a positive signal at least as bright as experimental cells to correctly determine spillover.
Question 4: In a compensation matrix for an 8-color panel, how many spillover values must be determined?
- 56 (Correct answer)
- 64
- 8
- 28
Correct answer: 56
For n colors, there are nĆ(nā1) = 8Ć7 = 56 off-diagonal spillover values in the compensation matrix.
Question 5: What effect does increasing PMT voltage have on the measured spillover coefficient?
- It has no effect if the detector is operating in the linear range (Correct answer)
- It increases the spillover coefficient proportionally
- It decreases the spillover coefficient
- It makes the coefficient detector-gain-dependent and unreliable
Correct answer: It has no effect if the detector is operating in the linear range
Spillover coefficients are ratios and remain constant across PMT voltages as long as detectors remain in their linear range.
Question 6: Which scenario would MOST invalidate a compensation control acquired from a previous experiment?
- The laser power was changed between experiments (Correct answer)
- A different operator collected the control
- The sample temperature differed by 2Ā°C
- A different lot of sheath fluid was used
Correct answer: The laser power was changed between experiments
Changes in laser power alter excitation and emission intensities, shifting the spillover coefficient and invalidating prior controls.
Question 7: In spectral cytometry, unmixing replaces traditional compensation; what serves as the equivalent of a single-color control?
- A reference spectrum for each fluorochrome (Correct answer)
- A matched unstained sample
- A tandem dye control
- A scatter-only beads sample
Correct answer: A reference spectrum for each fluorochrome
Spectral unmixing uses a full reference spectrum (emission profile across all detectors) for each fluorochrome instead of pairwise spillover values.
SCYM Compensation Techniques 2
In multicolor flow cytometry, what is the consequence of under-compensation for spectral spillover?