[Comparison between the value of urinary free cortisol and 17-hydroxycorticosteroids for the diagnosis of Cushing's syndrome].

The usefulness for the diagnosis of Cushing's syndrome of urinary free cortisol and urinary 17-hydroxycorticosteroid (17-OHCS) determination was compared by measuring these substances in 17 normal and 28 obese subjects and in 19 patients with established Cushing's syndrome. These measurements were repeated in 16 obese subjects and 11 Cushing's syndrome patients after oral administration of dexamethasone (2 mg/day for 2 days, then 8 mg/day for 2 days). As a group, the patients with Cushing's syndrome had higher (p less than 0.001) excretion rate of both free cortisol and 17-OHCS, but the values observed in this group overlapped with those of normal and obese subjects. The overlap was not significantly different for free cortisol and 17-OHCS excretion. In each obese subject, oral dexamethasone decreased the urinary excretion rate of both free cortisol and 17-OHCS. Seven out of the eleven patients with Cushing's syndrome had no decrease of urinary free cortisol or 17-OHCS, whereas both values were slightly lower in one and decreased to levels similar to those obtained in obese subjects in the three remaining patients. It is concluded that there is no advantage in measuring free cortisol excretion instead of 17-OHCS excretion, either before of after a pituitary-adrenal suppression test, for the diagnosis of Cushing's syndrome.