Recommendations for assessing commutability of a replacement batch of a secondary calibrator certified reference material

Commutable secondary certified reference materials (CRMs) play an essential role in the calibration hierarchy of many in-vitro diagnostic measurement procedures used in the medical laboratory. Therefore, sustainable availability of these CRMs is crucial to guarantee the long-term equivalence of results obtained for the clinical samples. The IFCC Working Group on Commutability in Metrological Traceability (WG-CMT) has published several recommendations for assessing the commutability of secondary calibrator CRMs. Performing a full commutability study according to these recommendations may present significant demands on the resources of CRM producers. This report provides recommendations for performing commutability equivalence assessments between existing CRMs of proven commutability and replacement batches of those CRMs. The approach evaluates the relationship of measurement results obtained with the relevant measurement procedures for the replacement batch versus the existing CRM batch. If this relationship is the same, the commutability properties of the replacement batch are considered equivalent to those of the existing CRM batch. Since the existing batch has a suitable commutability, the commutability of the replacement batch is also declared fit for purpose. Because this commutability equivalence assessment involves certain risks, a small number of representative clinical samples are included as safeguards. There are several prerequisites for performing the commutability equivalence assessment and producers of secondary CRMs will probably need to implement improvements before using this approach. However, once the improvements are implemented, the commutability equivalence assessment approach will significantly reduce the resources needed to maintain the supply of CRMs.