The goal of standardization for measurements of catalytic concentrations of enzymes is to achieve comparable results in human samples, independent of the reagent kits, instruments and laboratory where the procedure is carried out. To pursue this objective, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) has launched a project to establish a reference system in clinical enzymology. This system is based on three hinges: a) extensively evaluated and carefully described reference procedures, b) certified reference materials and c) a network of reference laboratories operating in a highly controlled manner. The original IFCC-recommended procedures for alanine aminotransferase, aspartate aminotransferase, creatine kinase, γ-glutamyltransferase, lactate dehydrogenase and α-amylase have been slightly modified to optimize them at 37 °C, with the definition of detailed operating procedures. A group of laboratories perform these procedures manually, with selfmade reagents on carefully calibrated instruments. Partially purified and stabilized materials, prepared in the past by the Community Bureau of Reference, have been re-certified by these laboratories for alanine aminotransferase, creatine kinase, γ-glutamyltransferase and lactate dehydrogenase activities. Using these materials and the manufacturer's standing procedures, industry can assign traceable values to commercial calibrators. Thus, clinical laboratories, which will use routine procedures with these validated calibrators to measure human specimens, can finally obtain values which are traceable to reference procedures.
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