Plasma corticosterone in dexamethasone suppression test on depressed patients.

We retrospectively assayed plasma corticosterone (B) in 143 dexamethasone suppression tests (DST) given serially to 19 depressed patients during the course of their hospitalization. A total of 424 blood samples from these 19 patients were analyzed for both plasma cortisol (F) and B. Concentrations of plasma B were not distributed normally. To establish a cut-off point for a positive B value in the DST, we log transformed the values for B to approximate a normal distribution. Using this approach we determined that a value of 1.3 ng/ml is the most sensitive cut-off point for the plasma B-DST in our laboratory. The serial DST's were performed weekly during the patients' stay and plasma B values were compared with plasma F values. Severities were assessed by weekly Hamilton ratings (17 items). In general, the B values closely parallel the F values. The sensitivity of F-DST was 53% (20/38) and the sensitivity was 56% (20/36) for B-DST. During treatment, both B and F normalized in parallel and this correlated strongly with improvements in the patients' severity ratings. These data confirm the fact that plasma B is as good (but not better) a marker for depression as plasma F in the DST.