Standardization by reference methods: a German viewpoint.

The problems of applying optimized as well as standardized methods to the determination of enzyme activities in modern clinical laboratories are described. The failure of the so-called 'New Concept of Reference Method Values' in the quality assessment of enzyme assays is evidenced, and the advantages of standardized methods rather than only standard materials is demonstrated. Finally, the great similarities among European national recommended methods for enzyme assay is emphasized by a comparison of results obtained in estimating 5 enzymes.