Quality control in clinical chemistry: characterization of reference materials

Reference serum preparations are key components of internal and external quality-control programmes. These materials are often poorly characterized, and use of inappropriate specimens may result in erroneous conclusions regarding quality of laboratory data. Several techniques are described that characterize specimens used in the quality-control or calibration of laboratory procedures. A characteristic approach requires detailed study of a few fundamental characteristics of reference preparations-such as steady-state kinetic properties of an enzyme-and comparison with the same parameters determined for patient specimens. Descriptive techniques-ratio methods and the multivariate statistical procedure of correspondence analysis-are used for further description of the interactions of materials in a variety of assay methods. The applications of these procedures to two clinical analytes-theophylline and alkaline phosphatase-are described.