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Commutability is a property of a reference material (RM) that relates to the closeness of agreement between results for an RM and results for clinical samples (CSs) when measured by ≥2 measurement procedures (MPs). Commutability of RMs used in a calibration traceability scheme is an essential property for them to be fit for purpose. Similarly, commutability of trueness controls or external quality assessment samples is essential when those materials are used to assess trueness of results for CSs. This report is part 1 of a 3-part series describing how to assess commutability of RMs. Part 1 defines commutability and addresses critical components of the experimental design for commutability assessment, including selection of individual CSs, use of pooled CSs, qualification of MPs for inclusion, establishing criteria for the determination that an RM is commutable, generalization of commutability conclusions to future measurements made with the MPs included in the assessment, and information regarding commutability to be included in the certificate for an RM. Parts 2 and 3 in the series present 2 different statistical approaches to commutability assessment that use fixed criteria related to the medical decisions that will be made using the laboratory test results.
© 2017 American Association for Clinical Chemistry
Background
A challenge in laboratory medicine is that lack of agreement between results among different measurement procedures (MPs)16 means that results may not be suitable for medical decisions based on those laboratory results. One of the contributors to lack of agreement is using noncommutable reference materials (RMs) as calibrators in the calibration hierarchy for clinical laboratory MPs. In this series of articles, we consider how to decide whether an RM has suitable commutability to be used as a common calibrator in the calibration hierarchy of MPs, as a trueness control material provided by an MP manufacturer to verify calibration, or as an external quality assessment (EQA) or proficiency testing sample. In this part, we describe the common requirements for the experimental design. In parts 2 and 3, we present 2 different statistical approaches for assessment of commutability. Part 2 is suitable for use when an RM is intended for use as a calibrator, a trueness control, or an EQA material (1 ). Part 3 is suitable for use only when the RM is...