The thyrotropin-releasing hormone test in the diagnosis of unipolar depression

The establishment of criteria for a blunted thyroid-stimulating hormone (TSH) response to thyrotropin-releasing hormone (TRH) may prove useful in distinguishing patients with major unipolar depression from patients with nonmajor depressions and controls. To this end, we administered the TRH test to a group of depressed, euthyroid inpatients diagnosed by Research Diagnostic Criteria and 20 normal volunteer controls. The mean maximal TSH response (delta TSH) to infusion of 500 micrograms of TRH of 7.3 +/- SD 4.6 microIU/ml in the 105 patients with major depressive disorder, primary unipolar subtype was significantly lower than that of 13.4 +/- SD 4.4 in the 20 controls and 10.9 +/- SD 4.4 in the 40 patients with nonmajor depressions. The differences were not explainable by differences in baseline thyroid function, age, or sex. When a delta TSH less than or equal to 7.0 microIU/ml was used as a diagnostic test for unipolar depression, the sensitivity of the TRH test was 56%, the specificity 93%, and the predictive value 91%. These results suggest that the TRH test may be useful in confirming the diagnosis of major unipolar depression and hence identifying patients likely to respond to antidepressant medications or electroconvulsive therapy.