IMPACT OF REFERENCE MATERIALS ON ACCURACY IN CLINICAL-CHEMISTRY

The analytical accuracy of the results of routine clinical chemistry m easurements is contributed by a two-steps mechanism, involving transfe rring trueness from a higher metrological and monitoring the time-stab ility of trueness itself. In both operations, different materials are used: however, accuracy in the routine assay of genuine patient sample s has to be the end product of this overall process. To such an aim, t he materials must show an intermethod behavior similar eo that of pati ent sera, i.e., they have to show commutability. Definitions of commut ability and methods for assessing such a property are mentioned. The f ollowing aspects of lack of commutability of materials are then discus sed: frequency; effects on the measured interlaboratory variability; a nd effects on the recalibration of analytical systems. The causes givi ng rise to lack of commutability are neither clear or easy to be shown . Matrix effect is one of the main causes; also, differences in the ch aracteristics of the component being measured are often responsible fo r noncommutability of materials for enzyme activity measurements. Exam ples of these two different situations are given. It is concluded that , for an efficacious overall quality assurance process, either a set o f minimally processed patient sera or commutable reference materials a re to be used in the operations concerned with the control of trueness . An additional alternative approach is based on the use of materials with system-specific assigned values. Copyright (C) 1998 The Canadian Society of Clinical Chemists.