Which factor would not cause shifts or trends in quality-control data?

• A. New lot numbers or reagents
• B. Change in laboratory personnel
• C. Outdated reagents
• D. Change in calibration of the instrument

Answer: (B)

Quality-control data are used to monitor whether the analytical system is performing consistently over time. A shift or a trend indicates a systematic change in the assay conditions. Changes to reagents (new lots or outdated reagents) and changes to instrument calibration are classic sources of such systematic shifts because they alter the measurement baseline or signal in a consistent way across runs. A change in laboratory personnel, on the other hand, is more about how the technique is applied. With proper training and strict adherence to standard operating procedures, operator-related variability tends to be random and nondirectional rather than producing a steady shift or trend in QC results. In other words, QC data are more sensitive to changes in reagents and instrument performance than to which technician is performing the test, so changing personnel would not inherently cause a sustained shift or trend.