Plasma corticosterone and cortisol following dexamethasone in psychiatric patients.

Radioimmunoassays of cortisol (F) and corticosterone (B) were carried out in 133 plasma specimens, obtained at 0800 or 1600 h on the day following administration of dexamethasone (1.0 mg), from 69 patients admitted to a psychiatric inpatient service, to test suggestions that assays of B might complement those of F in the dexamethasone suppression test (DST) in a psychiatric setting. The overall correlation between F and B was +0.80. Concentrations of B averaged 5-8% those of F. We found close agreement (80-85%) between positive (F greater than or equal to 4.5 micrograms/dl) and negative DST results for both steroids assayed by radioimmunoassay at a criterion of greater than or equal to 1.5 ng/ml for B, as well as a reasonable compromise between sensitivity and specificity of the B-DST at that criterion. Post-dexamethasone samples obtained at 1600 h showed somewhat closer agreement between the B-DST and the F-DST than at 0800 h. Inclusion of 0800 h samples added little to the rate of positive results with the F-DST but did add to those of the B-DST by about 10% or more, depending on the criterion selected for a positive B-DST. The rate of positive DSTs among 44 patients who had both steroids assayed at both times was approximately 61%, and the agreement between positive test results among these patients was 92%. In a mixed population of acutely ill, hospitalized patients with various DSM-III diagnoses, but excluding those with medical or pharmacologic contraindications to the DST, high rates of positive DST results were obtained in patients with major depressive disorders (47-58%), with little difference found among those with bipolar, non-bipolar or melancholic characteristics. High rates also were found among manic and other acutely psychotic patients, as well as others with neurotic or characterological diagnoses, but rarely in a small group of chronic schizophrenics. Thus, a positive DST as evaluated with B or F is evidently not specific for cases of major depression, but may be indicative of acute illness, possibly with affective features. The results support suggestions that a steroid suppression test based on corticosterone may be useful to aid in diagnosis of major psychiatric illnesses and might complement or substitute for the F-DST. It may be possible to avoid certain pharmacologic complications in the DST by use of a test based on suppression of B by F rather than by dexamethasone.