Distribution of patients' test values and applicability of "average of normals" method to quality-control of radioimmunoassays.

Applicability of the Hoffmann's average of normals (Mn) method was evaluated in quality control (QC) of radioimmunoassays (RIA) for thyroxine, 3,5,3'-tri-iodothyronine, thyrotropin, and insulin--assays that are performed routinely in the authors' laboratory. In the first three RIAs, the patterns of the distributions were almost constant and Mn showed significant correlations with values of QC sera and intercepts of the dose-response curve. In insulin RIA, the patterns varied appreciably and Mn showed correlations with parameters that reflect a disturbance in the distribution. Exclusion of assays with abnormal distributions, however, resulted in better correlations of Mn with other QC parameters. These results suggest that average of normals method can be a very useful adjunct to conventional QC methods for RIA. The possibility that the method may be affected by a disturbance in the distribution can be monitored by computation of parameters reflecting such disturbance.