CLINICAL AND ANALYTICAL EVALUATION OF AN IMMUNORADIOMETRIC ASSAY FOR CORTICOTROPIN

We evaluated a new IRMA developed commercially for the measurement of corticotropin (ACTH) in human plasma. The assay involves purified poly clonal goat capture antibodies specific for ACTH 26-39 and an I-125- l abeled monoclonal signal antibody specific for ACTH 1-17. CVs for intr aassay and total precision at ACTH concentrations between 9 and 801 ng /L ranged from 2.5% to 4.7% and from 3.3% to 9.3%, respectively, with an assay detection limit of 1.7 ng/L. The reference interval determine d for adults with the new method (16-52 ng/L) differed significantly ( P <0.05) from that for an established ACTH IRMA (9-54 ng/L). Method co mparison with clinical samples (n = 179) revealed a correlation coeffi cient of 0.970 and a best-fit equation of y (new IRMA) = (1.011 +/- 0. 019)x + (4.17 +/- 3.31) with S-ylx = 40.2. Both methods showed equival ent clinical sensitivity in evaluating Gushing disease, adrenal tumors , ectopic ACTH-producing tumors, hypopituitarism, steroid suppression, surgical adrenalectomy, Nelson syndrome, Addison disease, and cortico tropin-releasing hormone stimulation. We conclude that the new IRMA is technically simple to perform and provides a specific and sensitive m ethod for evaluating of adrenocortical function.