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The dexamethasone suppression test and depression. Approaches to the use of a laboratory test in psychiatry
Abstract:
The dexamethasone suppression test has undergone unprecedented study among the biologic tests proposed for clinical use in psychiatry. Since the 1970s, its study has involved hundreds of reports and thousands of patients. Although important technical aspects of the test appear to be well accepted and validated, additional information is needed regarding the pharmacokinetics of dexamethasone. Marked interindividual differences in plasma dexamethasone suggest that performance of the test might be improved by factoring dexamethasone levels into test interpretations. There also may be advantages to the development of a modified test involving other exogenous and index steroids, such as monitoring corticosterone levels. Although it is too early to determine how ROC analysis will alter the clinical application of the test, some implications for methodology and data presentation are already clear. First, because the test is a diagnostic system with nonbinary outcomes, ROC analysis can augment traditional performance indices such as sensitivity, specificity, and positive predictive power. Second, ROC analysis will improve comparisons between the studies of different research groups and will help assess innovations in the application of the test. Third, ROC analytic techniques permit appropriate planning of sample size given estimates of the expected values of AUC that would be obtained from the studies. ROC theory thus promises to play an increasingly important role in the evaluation and future improvement of the dexamethasone suppression test and other biologic markers in clinical psychiatry. In conclusion, neither uncritical enthusiasm nor excessive skepticism is warranted about the use of the dexamethasone suppression test in clinical psychiatry. Evidence to date should encourage investigators to pursue refinement of the test or other tests of hypothalamic-pituitary-adrenal functioning to increase their accuracy and clinical utility.