Improved radioimmunoassay for 11-deoxycortisol (compound S) in plasma.

We describe a radioimmunoassay for 11-deoxycortisol (Compound S) that involves preliminary chromatography on Sephadex LH-20, to isolate 11-deoxycortisol from crossreacting structurally related steroids. Pools with means of 3.4, 12.9, and 69.9 micrograms/L gave intra-assay coefficients of variation of 9.7, 9.6, and 11.4%, respectively; pools with means of 4.6, 27, and 95 micrograms/L gave inter-assay CV's of 10.1, 9.7, and 6.2%, respectively. A normal range (mean +/- 2SD) of 0.5 to 12.0 micrograms/L was obtained. This procedure is useful for the specific determination of 11-deoxycortisol, commonly determined in blood as part of the metyrapone test for assessing pituitary corticotropin reserve.