Demonstrating commutability of an existing certified reference material for use with an end-user measurement...

Commutability assessment of a certified reference material (CRM) intended for use as a secondary calibrator should be performed by the CRM producer at the time the material is originally prepared. Assessment typically includes several in-vitro diagnostic (IVD) measurement procedures (MPs) in common use in medical laboratories. Due to logistical constraints, it is usually not possible to include all existing IVD-MPs in a commutability assessment. In addition, a new IVD-MP (IVD-MP_n) may be introduced into the market after a commutability assessment was performed for a given CRM. Here we provide a recommendation how to assess commutability of an existing CRM for use with an IVD-MP_n that was not included in the original commutability assessment. The study design follows the same principles as a full commutability assessment, but it includes only the IVD-MP_n and fewer additional comparator MP(s) for which the CRM's commutability with clinical samples was previously demonstrated. When no reference measurement procedure (RMP) is available, or when the logistics make an RMP difficult to use, other IVD-MP(s) that were part of the original commutability assessment for the CRM should be used as comparator MP(s). When selecting a comparator IVD-MP, its performance must be carefully considered and its selectivity for the measurand should be equivalent to that of the IVD-MP_n. The CRM should have had negligible noncommutability bias with the comparator IVD-MP in the original commutability assessment. When the existing CRM meets the commutability criterion for IVD-MP_n, the CRM can be used in the calibration hierarchy of the IVD-MP_n.