Guidance on Which Calibrators in a Metrologically Traceable Calibration Hierarchy Must Be Commutable with Clinical Samples

Equivalent results for the same measurand in clinical samples (CSs), measured using different end-user in-vitro diagnostic medical devices (IVD-MDs), are essential for the application of clinical practice guidelines for diagnosis, treatment, monitoring, or risk assessment. The International Organization for Standardization (ISO) document 17511:2020 specifies how to establish metrological traceability to the highest available reference system component to enable equivalent results among IVD-MDs. Commutability with CSs is an essential property of a reference material used as a calibrator in a calibration hierarchy. However, not all calibrators in a calibration hierarchy are required to be commutable; different calibration hierarchies have different requirements for which calibrators must be commutable with CSs. Because assessment of commutability is a substantial effort, it is therefore important to determine which calibrators need to be commutable when implementing a calibration hierarchy. We provide guidance on which calibrators must be commutable with CSs, when a correction for any noncommutability bias is appropriate, and when commutability of a calibrator with CSs is not required for various types of calibration hierarchies described in ISO 17511:2020.