Lipidex chromatography in the radioimmunoassay of serum and urinary cortisol.

A highly specific method for the determination of cortisol in human serum and urine is described. The sample is first extracted with diethyl ether/ethyl acetate (1 : 1, by vol.), then chromatographed on a highly lipophilic derivative of Sephadex (hydroxyalkoxypropyl Sephadex, Lipidex) in light petroleum/chloroform (1 : 1, by vol.), and finally cortisol is measured by radioimmunoassay using a cortisol-21-BSA antiserum. Bound and unbound radioactivities are separated using dextran-coated charcoal technique. The 8 a.m. values (mean +/- S.D.) of cortisol among 11 young females and 16 young males were 152 +/- 32 ng/ml (range 111-235) and 185 +/- 21 ng/ml (103-232), respectively. The respective values at 4 p.m. were 84 +/- 29 ng/ml (26-117) and 84 +/- 36 ng/ml (32-172). The importance of Lipidex chromatography was demonstrated with assays of serum samples from children with congenital adrenal hyperplasia; without chromatography cortisol values were 6 times those with chromatography. Specific cortisol assays from pregnancy serum also necessitated Lipidex chromatography. Among 11 young men and 9 young women the mean daily urinary cortisol excretion was 56 +/- 26 mug (32-109) and 60 +/- 24 mug (39-109), respectively. Specific urinary cortisol determination could not be achieved without Lipidex chromatography.