Poly-maleic acid anhydride (PMA) coupled cortisol antibody in routine determination of urinary free cortisol.

Antibodies against cortisol-21-hemisuccinate conjugated to bovine serum albumin was raised in rabbits and conjugated with poly-maleic acid anhydride. The conjugate was used in a solid phase radioimmunoassay to measure the urinary excretion of unconjugated cortisol. Cortisol was extracted with methylene chloride, the extract purified by chromatography on Sephadex LH-20, and the cortisol content measured with the radioimmunoassay. The intra-assay variation of the method was 6 per cent and the interassay variation 10 per cent. In 95 normal adult persons the excretion of free cortisol was 11--70, mean 30 micrograms/24 h. No sex or age difference was found. In 8 children aged 7--14 years the excretion was 8--46 micrograms/24 h.