Comparison of 1mg versus 2mg Dexamethasone Suppression Test in Patients with Obesity

In this study, we compared the 2mg dexamethasone suppression test (DST) with the gold-standard 1mg DST in obese patients in order to reduce the false-positive rate for Cushing's syndrome (CS). The primary endpoint was the comparison of serum cortisol levels after 1mg versus 2mg DST in patients with a BMI >30kg/m (2) and at least one additional feature of the metabolic syndrome. Secondary endpoints were comparison of salivary cortisol and ACTH levels, respectively. Fifty-four obese patients were included. Median serum cortisol levels after 1mg DST and 2mg DST were similar [28nmol/l (20; 36) vs. 28nmol/l (20; 38), p=0.53]. Salivary cortisol was 8.2nmol/l (4.7; 11.7) after the 1mg DST vs. 6.7nmol/l (4.2; 9.5) after the 2mg test, p=0.09. ACTH levels were higher after the 1mg DST compared to the 2mg DST [10.0pg/ml (7.6; 10.7) vs. 5.0pg/ml (5.0; 5.1), p<0.0001]. The false positive rate after the 1mg DST was 14.8% (n=8) and was reduced to 11.1% (n=6) after the 2mg DST. All non-suppressors (n=8) had type 2 diabetes and most of them took a medication interacting with cytochrome P450 3A4 (CYP3A4). In individuals with obesity, the 2mg DST was not superior to the 1mg DST in regard to serum cortisol levels. However, in some patients, particularly with poorly controlled diabetes or medication interacting with CYP3A4 and without adequate suppression after the 1mg DST, the 2mg DST might prove helpful to reduce the false-positive rate for CS. ClinicalTrials.gov Number: NCT02227420