The 1977 College of American Pathologists Enzymology Survey. Principal findings.

A set of linearly related serum survey specimens was analyzed by more than 200 laboratories on four occasions in 1977 for the five enzymes lactate dehydrogenase, aspartate and alanine aminotransferases, creatine phosphokinase, and alkaline phosphatase. The survey technic, which employs specimens that are designed to have multiple informational redundancies for detecting discrepancies in the survey data, was found to be a feasible approach, as a variety of methodologic biases and analytic problems were readily detected. The specimens were shown to be stable,and the mean results obtained by a reference group of laboratories were quite reproducible. Consequently, changes observed in individual laboratories in successive surveys were attributable to intra-laboratory changes. The survey provides each participant with an objective evaluation of the linearity, precision, and calibration of his methods, in comparison with peer and reference laboratories, as well as information concerning the popularities of various methods, and the performances of various analytic systems. For each enzyme there are a few large peer groups and a large number of small peer groups. Differences among the laboratories within each peer group were due primarily to proportional biases that in some cases were clearly due to instrumental or reagent differences, rather than to methodologic differences.