Why Commutability Matters

Abstract

A fundamental goal of laboratory medicine is that results for patients’ samples will be comparable independent of the medical laboratory that produced the results. Routine measurement procedures of acceptable analytical specificity that have calibration traceable to the same higher-order reference material or reference measurement procedure should produce numerical values for clinical samples that are comparable irrespective of time, place, or laboratory generating the result. The term “commutability” was first used to describe the ability of a reference or control material to have interassay properties comparable to the properties demonstrated by authentic clinical samples when measured by more than one analytical method (1)(2)(3). More recent metrologic documents expand the concept; they describe commutability as the equivalence of the mathematical relationships between the results of different measurement procedures for a reference material and for representative samples from healthy and diseased individuals (4)(5). A reference material is typically used to establish or verify the traceability of a measurement procedure to a value assigned to the material that represents the best estimate of the correct, or true, value. Concentration or activity values are assigned to reference materials by higher-order measurement procedures, when possible, or alternatively by a consensus process when reference measurement procedures are not available. When a reference material is intended to be measured by a routine clinical method, commutability must be validated among all of the …