Enzyme immunoassay for serum 18-hydroxycorticosterone and its clinical application

An enzyme immunoassay for serum 18-hydroxycorticosterone was established using alkaline phosphatase as a label. The antiserum for 18-hydroxycorticosterone was produced by immunization of rabbits with 18-hydroxycorticosterone 3-(O-carboxymethyl)oxime conjugated to bovine serum albumin. Sephadex LH-20 column chromatography was used to separate 18-hydroxycorticosterone from other steroids in serum samples. The minimal detectable amount of 18-hydroxycorticosterone was 50 pg/tube and the measurable range was from 5 to 1000 ng/dl when a 1.0 ml serum sample was used. Intra- and inter-assay coefficients of variance were 5.0% (n = 6) and 5.8% (n = 6), respectively. Four of 5 patients with aldosterone-producing adenoma had above-normal serum 18-hydroxycorticosterone levels.