Clinical evaluation of the liquid-chromatographic determination of urinary free cortisol

We recently reported (Clin. Chem. 28: 1497-1500, 1982) a liquid-chromatographic method for quantifying free cortisol in urine. We have since evaluated the clinical utility of our method by assaying cortisol in urine from normal subjects, patients, and subjects undergoing endocrine tests. We found that, in contrast with plasma cortisol, urinary cortisol is not bound to protein. It shows some correlation with 17-hydroxycorticosteroids in urine, but is independent of creatinine excretion. The amount of cortisol excreted daily by a particular individual was found to be fairly constant during nine or 10 days. Normal values determined for 203 apparently healthy individuals were 35.8 (SD 18.7) micrograms/day, with no significant sex-related differences but a tendency for a gradual decrease of cortisol excretion with age. We also report urinary cortisol excretion by patients with pituitary-adrenal disorders and some other diseases, and the pattern of response to dexamethasone and metyrapone administration.