Clinical application of a sensitive immunoradiometric assay for human growth hormone

A sensitive immunoradiometric assay (IRMA) for human growth hormone (GH) using monoclonal antibodies was evaluated for clinical application. The detection limit of GH in serum was 0.05 ng/ml using 0.1 ml of serum. The specificity and assay precision were satisfactory. GH levels in serum determined by the IRMA were well correlated to those determined by the sensitive enzyme immunoassay or the commercial radioimmunoassay. Most of the basal GH levels in serum from normal adult subjects were detectable; mean values in male and female were 0.21 and 0.65 ng/ml, respectively. Serum GH levels decreased to less than 1 (0.5) ng/ml after oral glucose loading in normal subjects. Postoperative acromegalic patients were classified into two groups according to their GH responses to glucose. In group 1, GH levels were suppressed less than 1 ng/ml, suggesting normal GH dynamics. On the other hand, in group 2, GH levels remained elevated above 1 ng/ml, and postinhibitory rebound rise in serum GH after dopamine infusion was observed, suggesting the presence of residual adenoma tissues. Determination by sensitive IRMA of GH responses during oral glucose loading is useful for evaluating the activity of postoperative acromegaly.