Informed use of the dexamethasone suppression test.

Like all laboratory tests, the dexamethasone suppression test (DST) should be used as an aid to diagnosis in specified clinical contexts. The test is not appropriate for routine screening for all psychiatric patients; it is most useful in those with a clinical picture of endogenous or melancholic depression for whom treatment with antidepressant drugs or ECT is being considered. In such cases, normalization of the DST may precede and be prognostic of clinical improvement. By contrast, failure of the DST to normalize in hospitalized patients being considered for discharge may be an indicator of possible relapse. Factors that can invalidate the DST, producing spurious false-positive results, are described, and the general principles for sound clinical use of the DST as a laboratory test in psychiatry are summarized.