A more specific, liquid-chromatographic method for free cortisol in urine.

Currently used assays for urinary cortisol reportedly overestimate it, owing to cross-reacting substances. We describe here a method for separating and measuring by liquid chromatography cortisol extracted from urine. The method is specific for cortisol and as little as 5 ng per sample can be measured. Mean analytical recovery of added cortisol was 98.8% (SD 6.1%) and the coefficients of variation ranged from 3.1 to 4.7% (within-day) and from 7.1 to 14% (between-day). Mean (and SD) urinary excretion of cortisol for 45 normal men and women was 20.1 (SD 7.6) micrograms/24 h; for 29 children it was 14.1 (SD 6.0) micrograms/24 h. Results by radioimmunoassay were 1.4- to 4.3-fold greater than by this method, and results of the two assays did not correlate well (r = 0.59, p less than 0.01). We consider the present method to be a practical and specific assay for three cortisol in urine.