Recommendations for establishing metrological traceability for in vitro diagnostic measurement procedures intended to be used for whole blood samples.

In vitro diagnostic measurement procedures (IVD-MPs) are central to clinical decision-making. Consistent interpretation across different IVD-MPs and laboratories depends on equivalence of measurement results. Equivalence of measurement results is achieved by establishing metrological traceability to higher-order references for IVD-MPs. Commutable secondary certified reference materials (CRMs) play an essential role in the metrological traceability of many IVD-MPs. However, due to their instability and inhomogeneity, whole blood (WB) samples are often not suited as source material for preparation of CRMs making secondary CRMs commutable with WB clinical samples (CSs) very challenging to produce. This report describes scenarios for establishing metrological traceability of IVD-MPs intended to measure WB CSs: i) When secondary CRMs are available and can be measured by the WB IVD-MP. If these CRMs are not commutable due to differences in matrix with WB CSs, a noncommutability bias correction may be established and implemented in the calibration hierarchy; ii) When no secondary CRM is available but WB CSs with a value assigned by a reference or other measurement procedure (MP) can be obtained, these WB CSs can be used directly in the place of a commutable secondary CRM in the calibration hierarchy; iii) When no secondary CRM is available and WB CSs with a reference value or other MP assigned value cannot be obtained. The guidance provided supports laboratories, manufacturers and other stakeholders in selecting and implementing appropriate calibration hierarchies, thereby improving the reliability of measurements on WB CSs.