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"What changed?" is a good question to ask when QC problems arise. The error has already been classified as random or systematic which gives clues about what to investigate first.
Tip: When performing troubleshooting, use a systematic and logical approach in isolating the cause. Make only one change at a time and document each action taken.
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.
Random Error
The causes of increased random error are generally more difficult to determine because of their random nature. Random errors are more likely due to bubbles in the reagent, reagent lines, sampling or reagent syringes, an improperly mixed or dissolved reagent, pipette tips not fitting properly, a clog in the pipettor, imprecise pipettor, the power supply, and even power fluctuations.
Many of these problems can be detected by inspecting the machine during operation. If a careful inspection provides no clues, consult the manufacturer's troubleshooting guides and recommendations.
If a run is repeated and the controls are acceptable but concern remains that a problem still exists, perform a precision run using ten back-to-back determinations on the same patient sample. This precision run may help identify further imprecision problems. Duplicate analysis of patient specimens is also recommended when monitoring random error problems.
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