Systematic Error

If a sudden shift is observed, inspect the reagent, calibration, and maintenance records, and note any recent actions. For example, if the shift occurred immediately following a reagent replacement, verify the lot number is correct, that it has been checked out or calibrated, that the reagent has been properly prepared, and the reagent is indeed the correct reagent.

If a systematic trend is observed, review the QC records, including documentation of function checks prior to taking actions to resolve the cause. Trends can be caused by a slowly deteriorating reagent, a calibration shift, a change in instrument temperature, or a deteriorating filter or lamp. Unfortunately, systematic trends can be more difficult to resolve than shifts because they occur over a longer time period.