What is a common cause of a shift in control charts?

A common cause of a shift in control charts is related to the changing lot numbers of reagents without recalibrating. When a laboratory uses a new lot of reagents, it is essential to recognize that different lots may exhibit variations in performance characteristics such as sensitivity and specificity. If the laboratory does not recalibrate its instrumentation or validate the new lot adequately, this can lead to systematic errors and shifts in the control limits of the quality control charts. Control charts are designed to monitor the stability of laboratory processes, and failing to adjust for differences in reagents can disrupt this stability, resulting in a significant and consistent shift in the plotted control points.

In contrast, fluctuations in lab temperature, while potentially affecting assay performance, typically lead to random variations rather than systematic shifts in control charts. Errors in data entry processes can introduce sporadic outliers or random errors rather than persistent shifts in the data. Variation in patient demographics may impact the overall results but typically does not lead to systematic changes in the control processes unless those demographics directly influence the assay performance in a predictable manner. Hence, changing reagent lots without recalibration is a specific cause that can definitively result in a shift in control charts.