A guest post by Nils Person, PhD, FACB
I recently read the essay "The QC We Really Do" with great interest and found the information very useful. However, there was one topic that I was concerned about. It had to do with re-calibration in response to QC rule failure. The essay indicated that re-calibration is a common response to QC rule failure.... and I am not sure that is a good strategy. .
Re-calibration is usually done to address gradual changes over time in the reagents or the instrument. These normal expected changes are the reason for periodic re-calibration as recommended by manufacturers. If this type of change is the root cause for the QC rule failure, then re-calibration is a good response to the QC rule failure.
However, this is an uncommon reason for QC rule failure for most methods on most instruments today. It does happen, but it's infrequent if the method is being calibrated according to manufacturer's recommendations. If the observed QC rule failure does indicate a true system problem, it is more likely that it has a different root cause. Therein lies the problem with re-calibration as a first line response to QC rule failure.
Calibration is, by it's very nature, designed to compensate for any bias in the instrument/method to allow it to accurately recover the "true" value of the sample tested. It does this by matching the signal measured when testing the calibrator(s) to the assigned value of the calibrator(s) and creating the calibration curve. If there is an unresolved problem with the method or the instrument, re-calibration will attempt to compensate for that problem. In essence to cover it up.
If the underlying problem is significant enough, the calibration process will fail and we will look for the problem elsewhere. This is fine. However, it is possible, and it has happened, that there may be an underlying problem that is modest, or is developing, but was detected by a well designed QC protocol. In this case, if we re-calibrate in response to the QC rule failure, we cover the problem up but do not solve it. The QC tested immediately following re-calibration will be acceptable because the calibration process has temporarily compensated for the unresolved problem. Unfortunately, the problem still exists and may continue to impact results. If the unresolved problem continues to develop, it may impact the quality of patient results and go undetected until the next time QC samples are tested. Then, we re-calibrate again and the cycle starts over until the next QC rule failure .... and round and round we go until the calibration process can no longer compensate for the problem. This is not desirable for the quality of lab results or the overall efficiency of the laboratory. It can lead to many unnecessary calibrations wasting time and materials, increasing TAT, and frustrating laboratory staff.
With most systems in use today, calibration drift is one of the least likely root causes for QC rule failure. Certainly there are specific methods from time to time that have had issues with calibration drift. So it can happen, but it is not a common problem. All too often when re-calibration is used as the first line response to QC rule failure, the continuing changes in method performance due to the unresolved actual root cause is misinterpreted as "calibration drift". In these cases, the continued use of re-calibration as the first response for QC rule failure just prolongs the time to resolution.
When QC rule failure occurs, the best strategy is to use patterns in the QC results, a review of what events have occurred since the last acceptable QC results, and similar troubleshooting practices to identify the root cause, rather then immediately resort to re-calibration. Otherwise, we only delay effective troubleshooting and negatively impact overall result quality. If the investigation uncovers a root cause that can be effectively corrected by re-calibration, then it makes sense. The obvious example would be unacceptable QC results immediately following a routine calibration of the method. Clearly, the most likely root cause is the recent calibration and the most effective response is to re-calibrate after investigating why the earlier calibration failed. So when QC rule failures occur, don't immediately reach for the calibrators. You'll save yourself time and trouble if you look for the real root cause instead.
Nils Person, PhD, FACB
Senior Scientist
Global Product Education
Siemens Healthcare Diagnostics
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