[Measurement of enzyme activity of control materials containing human enzymes by IFCC reference methods]

In order to unify interlaboratory clinical enzyme data, a reference method and reference material are necessary for each enzyme. Although reference methods recommended by various societies of clinical chemistry including JSCC are now available for some routinely measured clinical enzymes, the availability of secondary enzyme references or calibrators, limits the practical application of standardization concept for minimizing present interlaboratory variation of enzyme data. Since control sera prepared by adding enzymes from human cell cultures to a pool of human serum may meet the requirements as candidates for such reference materials, we attempted to assign values to 6 enzymes present in the materials by mainly the IFCC reference methods following the procedures as strictly as possible and yet with modifications where necessary. This paper describes each step of the value assignment for accuracy control purposes.