IFCC Working Group Recommendations for Assessing Commutability Part 1: General Experimental Design

Abstract

Commutability is a property of a reference material (RM) that relates to the closeness of agreement between results for an RM and results for clinical samples (CSs) when measured by ≥ 2 measurement procedures (MPs). Commutability of RMs used in a calibration traceability scheme is an essential property for them to be fit for purpose. Similarly, commutability of trueness controls or external quality assessment samples is essential when those materials are used to assess trueness of results for CSs. This report is part 1 of a 3-part series describing how to assess commutability of RMs. Part 1 defines commutability and addresses critical components of the experimental design for commutability assessment, including selection of individual CSs, use of pooled CSs, qualification of MPs for inclusion, establishing criteria for the determination that an RM is commutable, generalization of commutability conclusions to future measurements made with the MPs included in the assessment, and information regarding commutability to be included in the certificate for an RM. Parts 2 and 3 in the series present 2 different statistical approaches to commutability assessment that use fixed criteria related to the medical decisions that will be made using the laboratory test results.

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

“…The commutability assessment determines whether the difference in bias plus its uncertainty fulfills the criterion for a conclusion that an RM is commutable, noncom-mutable, or indeterminate for pairs of MPs. Conclusions regarding suitability for use of an RM can be made by assessing its commutability for all MPs in the assessment as described in part 1 of this series (1). …”

“…The precision and selectivity of each MP should be known in advance and considered in the experimental design. As explained in part 1 of this series (1), MPs should be prequalified for inclusion in a commutability assessment, and MPs with inadequate performance should be excluded. However, sample-specific differences are estimated in this commutability assessment experimental design and, when excessive, can be a reason to exclude an MP from the data analysis and to declare that the RM is not suitable for use with that MP.…”

“…The conclusions about commutability of the RM are generalized to all future results using other IVD medical devices representative of the same MP with the assumption that other IVD medical devices have equivalent performance when operated under conditions such as different reagent and calibrator lots, maintenance, and operators. Limitations of this assumption were discussed in part 1 of this series (1). …”

“…Commutability was defined in part 1 of this series (1). This second part describes a statistical procedure to assess commutability based on the difference in bias between a reference material (RM) 16 and clinical samples (CSs) measured using 2 different measurement procedures (MPs).…”

“…As explained in part 1 of this series (1), an MP refers to a written specification for how a measurement is performed. A measuring system is a physical in vitro diagnostic (IVD) medical device manufactured according to the MP specifications and used to make measurements on CSs.…”