In most circumstances, when two controls within a run are both greater than ±2s from the mean, what action should be taken first?

• A. Recalibrate, then repeat controls followed by selected patient samples if quality control is acceptable
• B. Repeat the controls before taking any corrective action
• C. Change the reagent lot, then recalibrate
• D. Prepare fresh standards and recalibrate

Answer: (A)

When quality control results show two controls outside the acceptable range, look for a systematic error, often due to instrument drift or calibration issues. The first action is to recalibrate the instrument to restore the correct relationship between signal and concentration. After recalibration, re-run the controls to confirm they are within acceptance limits. If they are acceptable, you can proceed with the selected patient samples. If not, you continue troubleshooting (repeat controls and check reagents, setup, or other potential causes) rather than changing reagents or standards as the initial step.