Smita K. Baid MD, Domenica Rubino MD, Ninet Sinaii PhD, MPH, Sheila Ramsey PhD, Arthur Frank MD, and Lynnette K. Nieman MD*
The Program in Reproductive and Adult Endocrinology, The Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA; The George Washington University Weight Management Program, Washington, DC, USA; Washington Center for Weight Management and Research, Arlington VA, USA; Biostatistics & Clinical Epidemiology Service, Clinical Center, National Institutes of Health, Bethesda, MD, USA
* To whom correspondence should be addressed. E-mail: NiemanL@nih.gov.
Context: Recent reports suggest a higher prevalence (1–5%) of Cushing's syndrome in certain patient populations with features of the disorder (e.g. diabetes), but the prevalence in the overweight and obese population is not known.
Objective: To evaluate the diagnostic performance of screening tests for Cushing's syndrome in overweight and obese subjects with at least two other features of the disorder.
Design and Setting: Cross-sectional prospective study.
Subjects and Methods: 369 subjects (73% female) completed two or three tests: a 24h urine cortisol (UFC), and/or late-night salivary cortisol, and/or 1 mg dexamethasone suppression test (DST). If any result was abnormal (based on laboratory reference range or cortisol after DST ? 1.8 ug/dl [50 nmol/l]), tests were repeated and/or a dexamethasone-CRH (dex-CRH) test was performed. Subjects with abnormal DST results and a low dexamathasone level were asked to repeat the test with 2mg of dexamethasone.
Results: In addition to obesity, subjects had a mean of 5–6 features of Cushing's syndrome. None was found to have Cushing's syndrome. Test specificities to exclude Cushing's syndrome for subjects who completed 3 tests were: UFC 96% [95 CI: 93–98%]; DST 90% [95 CI: 87–93%]; salivary cortisol 84% by RIA [95 CI: 79–89%] and 92% by LC-MS/MS [95 CI: 88–95%]. The combined specificity (both tests normal) for all combinations of two tests was 84 to 90%, with overlapping confidence intervals.
Conclusion: These data do not support widespread screening of overweight and obese subjects for Cushing's syndrome; test results for such patients may be falsely abnormal.
Key words: Cushing's syndrome • dexamethasone • diagnosis • obesity