Dexamethasone suppression test (DST) and plasma dexamethasone levels in depressed patients.

The dexamethasone suppression test (DST) was evaluated in newly hospitalized patients with a DSM-III diagnosis of major depression. Patients with other psychiatric disorders and a normal control group were also studied. Plasma dexamethasone levels were obtained in all patients, and the relationship between plasma cortisol and plasma dexamethasone was examined. Rates of non-suppression in patients with major depression (39%) were not significantly different from those in patients with minor depression (25%), mania (38%), or other psychiatric illnesses (17%). The ranges of dexamethasone levels at 8 a.m. and 4 p.m. were similar between patient groups and controls. However, there was a significant difference in dexamethasone levels between suppressors and nonsuppressors, irrespective of diagnosis, which could not be explained by differences in weight or plasma dexamethasone half-life. Inappropriately high dexamethasone levels were found in some patients with a 1 mg test, a problem that critically affects the sensitivity of the test procedure.