Quality control of testosterone and digoxin radioimmunoassays and cortisol competitive protein binding assay by the reference sample method.

The inclusion of a minimum of 2 reference samples in the radioimmunoassay of testesterone and digoxin, and the competitive protein binding assay of cortisol served as a simple and practical index of overall assay performance. Statistical parameters, the mean plus or minus 2 standard deviation limits as well as the % coefficient of variation were determined at 3 clinically significant values for these samples. While a 50% intercept served mainly to indicate standard curve sensitivity, quality control sera provided a valid assessment of annay precision.