Limited Utility of the 1-mg Dexamethasone Suppression Test as a Measure of Hypercortisolism

To the Editor.—  In the article by Stokes et al₁ about a multicenter study of the 1-mg dexamethasone suppression test (DST), the authors reported a very high percentage of abnormal test results in healthy subjects (35%, when three post-DST blood samples were used) and no close linkage between DST nonsuppression and cortisol hypersecretion (measured by urinary free cortisol excretion every 24 hours). Previous studies with 2 mg of dexamethasone, however, revealed a much lower rate of DST nonsuppression in healthy subjects₂ and found an abnormality of 2 mg of DST to be a highly specific, although not very sensitive, indicator for hypercortisolism.₃ Taken together, these results suggest that a dose of 1 mg of dexamethasone is too low to provide reliable DST results. We have recently performed 160 1-mg DSTs in 93 psychiatric inpatients who had different psychiatric diagnoses.₄ The post-DST plasma cortisol level was measured at 9 AM,