Internal Quality Control in Medical Laboratories: Westgard and the Others

This review recalls some ISO 15189:2022 requirements for the management of examination results and emerging alternatives to internal quality control (IQC) in relation to Italian Society of Clinical Pathology and Laboratory Medicine (SIPMeL) Recommendation Q19. We observed phenomena of contrasting “metrological”, or rather “tracealogic”, and “statistical” approaches. SIPMeL Recommendation Q19 enhances IQC with a moving average based on ISO 15189, which enables the use of the moving average of patient sample results (MA). In the veterinary field, the procedure of QC with repeat testing on patient samples (RPT-QC) has met with some success. The “Bayesian approach” of IQC makes use of the distinction between a priori probability, evidential probability (data) and a posteriori probability (IQC rules). SIPMeL Recommendation Q19 strictly adheres to the ISO 15189:2022 document. SIPMeL Q19 calls for abandoning the 1–2 s rule, using appropriate computer tools, not only control charts, and trying to reduce false positives to very low frequencies. Alternatives to IQC using patient results and the Bayesian approach are compatible with ISO 15189 and SIPMeL Q19. In contrast, the alternative using material designed for traceability with assigned values, is not compatible with the ISO standard.