Six Sigma-based quality control leaning guide series

It is standard practice in the clinical lab to test quality control (QC) samples (typically called “controls”) at least daily and, preferably, multiple times per day. Controls are necessary to ensure analytical systems are of sufficient quality and “fit for purpose” because the performance of even the best assays can change over time. Statistical quality control (SQC) practices have long been established for this purpose.

However, once QC practices are established, there’s a tendency to accept them without question and to continue to follow routine algorithms without periodic critical re-examination of their appropriateness. A one-size-fits-all approach, such as testing two controls once a day, is common, but it’s a minimal practice. Such a simple QC rule is easy to follow, but it ignores the fact that not all assays are of equal analytical quality. An optimal QC program recognizes the need for customized QC rules for assays based on their inherent variability and establishes practical