IFCC Working Group Recommendations for Assessing Commutability Part 3: Using the Calibration Effectiveness of a Reference Material

A process is described to assess the commutability of a reference material intended for use as a calibrator based on its ability to fulfill its intended use in a calibration traceability scheme to produce equivalent clinical sample results among different measurement procedures for the same measurand. Three sources of systematic error are elucidated in the context of creating the calibration model for translating measuring system signals to measurand amounts: calibration fit, calibrator level trueness and commutability. An example set of 40 clinical sample results from seven measuring systems is used to illustrate estimation of bias and variability for each measuring system. The candidate reference material is then used to recalibrate each measuring system, and its effectiveness to reduce the systematic error among the measuring systems to an acceptable criterion for equivalence based on medical requirements confirms its commutability for those measuring systems. The reference material is declared non-commutable for measuring systems for which after recalibration the clinical sample results do not agree with those from other measuring systems. When a non-commutable conclusion is reached, the measurement procedure calibration model should be investigated as a possible cause for the limitation before concluding the reference material is non-commutable. The reference material is considered fit for purpose for those measuring systems where commutability is demonstrated.JRC.F.6-Reference Material