Dexamethasone suppression test for depression.
The DST is a practical laboratory test that can be used in outpatient or inpatient settings. The required laboratory technology is available at any hospital. No subjective, behavioral, or metabolic side-effects occur with the single-dose administration of dexamethasone, and the test is well tolerated by patients. The test is not affected by most of the usual psychotropic drugs, and no special dietary precautions are needed. The recommended procedure for inpatients yields good sensitivity (67%) and high specificity (96%). Like many laboratory tests, the DST will be most useful if there is a moderate probability that the disorder being considered (melancholia) is actually present (4). If the prevalence of melancholia in the population tested is at least 35%, then the predictive value (diagnostic confidence) of an abnormal test result will be at least 90%. If the prevalence is very low, however, then the predictive value also will be much lower. Thus, the DST is not suitable for screening unselected patients but should be used when the clinician thinks it might help to answer a specific diagnostic question. Several clinical applications of the DST are being developed, as outlined above. All of these proposed uses of the test need further study. As the test is used more widely, an important principle to remember will be that physicians treat patients, not laboratory results; the test results always should be interpreted in clinical context. Provided that the principles of application discussed above are observed, then the DST has real potential for aiding clinicians in the diagnosis and management of depressed patients. Given the known unreliability of clinical diagnoses, it will not be surprising to find that the laboratory test result causes clinicians at times to reevaluate their patients and to recognize treatable depressions that were previously overlooked.
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