Do serum dexamethasone levels improve the DST?

Some investigators have reported that dexamethasone suppression test (DST) accuracy might be improved by incorporating dexamethasone concentrations ([dex]) into test results. Using receiver operating characteristic methods, we evaluated data from four studies in which cortisol and dexamethasone levels were measured simultaneously at one or more times after drug ingestion. We compared DST accuracy using cortisol alone with various diagnostic indices incorporating [dex]. In none of the 21 comparisons did the [dex] factor enhance diagnostic performance.