Maximizing Diagnostic Information From the Dexamethasone Suppression Test

Data from seven published studies is employed to demonstrate how ROC analysis may be used to characterize the discriminative properties of the dexamethasone suppression test (DST) and to select cortisol cutoff levels with the highest information content for each of the DST studies.

Abstract

Receiver operating characteristic analysis yields indices of diagnostic performance that permit innovative mathematical descriptions and comparisons of diagnostic tests whose results are distributed over a range of possible outcomes. We employed data from seven published studies to demonstrate how ROC analysis may be used to characterize the discriminative properties of the dexamethasone suppression test (DST). We also used an intrinsic property of test results--their ability to reduce diagnostic uncertainty--to select cortisol cutoff levels with the highest information content for each of the DST studies. These cutoffs often differ from original authors' definitions of nonsuppression. The information-maximizing cortisol levels vary depending on pretest estimates of the prevalence of depression or melancholia and vary among studies. Receiver operating characteristic analytic techniques provide important tools for a full description of the DST. Future studies should use receiver operating characteristic methods to select cortisol cutoffs and to assess the test's overall performance.