The Paradigms and Paradoxes of Sigma Metrics in the Analytical Phase of the Medical Diagnostic Laboratory

William Osler very aptly described healthcare in his statement "Medicine is a science of uncertainty and an art of probability". Since 70% of patient related medical decisions are based on reports from the medical diagnostic laboratory, the latter must implement good laboratory practices and stringent quality control measures to minimize uncertainty. Towards this, medical diagnostic laboratories use the sigma metric statistical tool to assess and maintain their quality performance. However, it needs to be emphasized that these tools were formulated for the manufacturing industry and hence, should be adapted to the medical laboratory's environment. This review is to familiarize the laboratorians with the basis of these tools and where one may need to deviate from their conventional acceptance and utilization.