The application of a new highly-sensitive radioimmunoassay for plasma 21-deoxycortisol to the detection of steroid-21-hydroxylase deficiency.

21-deoxycortisol (21-DF) is a steroid of strictly adrenal origin formed by the 11-hydroxylation of 17-hydroxyprogesterone. This metabolic pathway is minor in normal subjects, in whom basal plasma concentrations range from 0.03 to 0.63 nmol/L and from 0.865 to 1.50 nmol/L after adrenocorticotrophic hormone (ACTH; Synacthène Immédiat, Ciba/Geigy, France). However, this metabolic pathway becomes major in 21-hydroxylase-deficient patients: in those who have the classical form of congenital adrenal hyperplasia (CAH) basal plasma 21-DF levels can attain more than 144 nmol/L. The synthesis of two isomers, E and Z, of the 21-deoxycortisol-3-carboxymethyloxime (CMO) hapten enabled us to prepare the corresponding E and Z immunogens by coupling them to bovine serum albumin (BSA), as well as the corresponding iodinated E and Z 21-DF-3-CMO-histamine tracers. We developed a very sensitive radioimmunoassay for 21-DF in plasma by associating an anti-21-DF-3-CMO-BSA-E isomer antibody to an iodinated 21-DF histamine-Z isomer (standard curve IC 50 = 8 pg/tube). This plasma 21-DF radioimmunoassay allowed diagnosis of the classical form of CAH in untreated newborn (basal 21-DF levels greater than 144 nmol/L), as well as the late-onset form (post-ACTH 21-DF levels greater than 11.54 nmol/L), and also permitted detection of 21-hydroxylase-deficient heterozygotes of both forms of CAH among the general population (post-ACTH 21-DF levels between 2.02 and 9.52 nmol/L).