False elevation of plasma cortisol in congenital adrenal hyperplasia.

Plasma cortisol values in seven patients with the 21-hydroxylase variant of CAH ranged from 9 to 35 micron/100 ml. (mean+/-S.E.=22+/-4) as determined fluorimetrically and from 22 to 35 microng/100 ml. (26+/-2) by competitive protein-binding radioassay. In these same patients the cortisol values obtained after Sephadex LH-20 column chromatography were much lower, ranging from 1 to 12.5 microng/100 ml. (5+/-2, p less than 0.01). In six normal subjects, cortisol values were similar before and after chromatography. Plasma concentrations of progesterone, 17alpha-hydroxyprogesterone, and 21-deoxycortisol in the CAH patients were increased 10 to 100-fold. The elevated cortisol values determined by customary methods were shown to be due to cross-interference of these and other steroids in the assays. Plasma cortisol values obtained routinely are falsely elevated and therefore misleading as a gauge of adrenal insufficiency in CAH.