Urinary free corticoids: an evaluation of their usefulness in the diagnosis of Cushing's syndrome.

We evaluated the usefulness of measurement of urinary free corticoids (UFC) in the diagnosis of hypercorticism. One hundred and thirty patients with features suggestive of Cushing's syndrome were examined. Twenty-six patients were proved to have Cushing's syndrome. The remaining 104 patients were considered not to have this disease on the basis of other investigations, and were designated as 'suspected patients'. UFC and 17-hydroxycorticosteroids were measured in all these patients in the basal state and on the 5th day of a low-dose-dexamethasone suppression test (3 mg/day for 5 days). UFC values of patients with Cushing's syndrome were well above 125 micrograms/24 h in the basal state and higher than 10 micrograms/24 h during the suppression test. UFC values of 'suspected patients' were between 20 and 125 micrograms/24 h in the basal state and below 10 micrograms/24 h during the suppression test. It can be concluded that the measurement of UFC in the basal state and on the 5th day of a suppression test is not only a very sensitive but also a specific method for the diagnosis of Cushing's syndrome.