Interlaboratory survey of enzyme analyses. I. Preliminary.

Enzyme survey specimens were prepared by spiking portions of a normal serum pool with creatinine, urea, and five enzymes (lactate dehydrogenase, creatine phosphokinase, alkaline phosphatase, and aspartate and alanine aminotransferases), and preparing admixtures of the spiked pools with the original serum. This admixture technic established linear interspecimen relationships that could be confirmed by analyses for creatinine and urea nitrogen. Both ethylene glycol-stabilized liquid serum specimens and lyophilized specimens were prepared as sets of six to eight samples having six concentrations of each enzyme. The sets were distributed on five occasions to about ten laboratories that were widely separated geographically, and the specimens were analyzed by a variety of methods, by various instrumental systems, and in different reaction conditions, and results were reported in diverse units. This report describes how the analytic data obtained through the use of these specimens that were specifically designed for survey purposes can be analyzed statistically to provide meaningful assessments of laboratory performance in enzyme analyses.