Interlaboratory survey of enzymatic analyses. II. Intermediate studies.

A set of six interrelated specimens was analyzed for creatinine, urea, and five enzyme constituents by about 10 laboratories on two occasions. The results from each laboratory were subjected to linear regression analysis and the correlation coefficients, X and Y intercepts, and slopes were calculated. These parameters then were used in various ways to (a) evaluate the composition, linearity and stability of the specimens, (b) assess the analytic precision of each laboratory, (c) assess the accuracy of the laboratories relative to their peer group, and (d) identify systematic differences among peer groups. The results suggest that this technic is a viable approach to the evaluation of laboratory performance in enzymatic analyses.