IFCC Working Group Recommendations for Assessing Commutability Part 2: Using the Difference in Bias between a Reference Material and Clinical Samples

TLDR

The paper proposes a method to evaluate the commutability of a reference material by comparing the bias difference between the RM and clinical samples across two measurement procedures. The method compares the RM–clinical sample bias difference to a medically relevant criterion, performs pairwise comparisons across all measurement procedure combinations, and uses an error model to estimate random and systematic error sources, including sample‑specific effects. The approach enables a single criterion for all measurement procedure combinations, accurately estimates the bias difference and its uncertainty, and declares an RM fit for purpose when commutability is demonstrated.

Abstract

Abstract A process is described to assess the commutability of a reference material (RM) intended for use as a calibrator, trueness control, or external quality assessment sample based on the difference in bias between an RM and clinical samples (CSs) measured using 2 different measurement procedures (MPs). This difference in bias is compared with a criterion based on a medically relevant difference between an RM and CS results to make a conclusion regarding commutability. When more than 2 MPs are included, the commutability is assessed pairwise for all combinations of 2 MPs. This approach allows the same criterion to be used for all combinations of MPs included in the assessment. The assessment is based on an error model that allows estimation of various random and systematic sources of error, including those from sample-specific effects of interfering substances. An advantage of this approach is that the difference in bias between an RM and the average bias of CSs at the concentration (i.e., amount of substance present or quantity value) of the RM is determined and its uncertainty estimated. An RM is considered fit for purpose for those MPs for which commutability is demonstrated.