ABSTRACT
Objective To reinvestigate the value of overnight low-dose dexamethasone suppression test in the diagnosis of Cushing syndrome.Methods Fifty-two patients with Cushing syndrome and 153 patients with simple obesity or essential hypertension in whom Cushing syndrome was excluded were studied retrospectively in order to compare the sensitivity and specificity of different serum cortisol cut-off levels in overnight 1 mg dexamethasone suppression test in the diagnosis of Cushing syndrome.Results The sensitivity of 50% of basal serum cortisol level at 8:00 and of the serum cortisol cut-off levels of 275,200,138,50 nmoL/L at 8:00 after the overnight 1 mg dexamethasone suppression test was 92.3%,92.3%,92.3%,92.3% and 100.0% respectively, and the specificity was 90.8%,98.7%,96.1%,91.5% and 78.4%,respectively.Conclusion The serum cortisol cut-off level of 50 nmol/L in the overnight 1 mg dexamethasone suppression test has very high sensitivity and can be used as a screening test for Cushing syndrome.