Automated approach to radioimmunoassays of somatotropin (human growth hormone) and insulin.

The adaptation of human somatotropin and insulin assays to the automated Centria radioimmunoassay system [Clin. Chem. 21, 1305 (1975)] is reported. For the somatotropin assay, reaction conditions include a borate/bovine serum albumin buffer (pH 8.4) AND 20-H Incubation at 4 degrees C. Assay results for clinical samples compared favorably (correlation coefficient = 0.930) with values obtained from a reference laboratory. The means determined for 92 patients' samples were 4.3 mug/liter (reference laboratory) and 5.1 mug/liter (Centria). Intra- and inter-run precision ranged from 3.2 to 15.9%. For the insulin assay, a phosphate/bovine serum albumin buffer (pH 7.4) is used, with a 20-h incubation at 4 degrees C. Previously analyzed insulin samples from a reference laboratory were determined by the Centria analyzer with excellent correlation (r = 0.965). Means for patients' samples were 43.0 milli (USP) units of insulin per liter (reference laboratory) and 47.5 milliunits of insulin per liter (Centria). In both assays an anionicexchange gel is used in the separation step. The criterion of parallelism, an indication of the validity of a radioimmunoassay, was satisfied in both assays. The Centria radioimmunoassay system offers the advantage of automating all the critical steps of these radioimmunoassays.