Exp Clin Endocrinol Diabetes 2006; 114(7): 356-360
DOI: 10.1055/s-2006-924281

J. A. Barth Verlag in Georg Thieme Verlag KG Stuttgart · New York

An Update on the Overnight Dexamethasone Suppression Test for the Diagnosis of Cushing's Syndrome: Limitations in Patients with Mild and/or Episodic Hypercortisolism

T. C. Friedman1
  • 1Division of Endocrinology, Metabolism, and Molecular Medicine, Charles R. Drew University, Los Angeles, CA, USA
Further Information

Publication History

Received: August 16, 2005 First decision: February 23, 2006

Accepted: March 16, 2006

Publication Date:
16 August 2006 (online)


The overnight one-mg dexamethasone suppression test has been used for many years to screen for Cushing's syndrome. This test has usually been evaluated in controls versus patients with severe hypercortisolism. Under these conditions, the overnight dexamethasone suppression test has been reported to have high sensitivity and specificity. The objective of this study was to determine the sensitivity of the one mg overnight dexamethasone suppression test in patients with mild and/or periodic Cushing's syndrome. Therefore, an overnight dexamethasone suppression test was performed in 17 consecutive patients presenting to an endocrinology clinic with signs and symptoms of hypercortisolemia who were later proven to have Cushing's syndrome. The majority of patients were found to have both mild and periodic hypercortisolism. One mg of dexamethasone was given at midnight and a plasma cortisol was measured by radioimmunoassay at 08:00 the following morning. Using a cut-off for a morning cortisol following overnight dexamethasone of > 5 µg/dL, only three of 17 patients failed to suppress to a value less than this cut-off (sensitivity 18 %). A cut-off of > 2 µg/dL gave similar sensitivity. Even with a stringent cut-off point of > 1.8 µg/dL, only seven of 17 patients failed to suppress to a value less than this cut-off point (sensitivity of 41 %). These results demonstrate that the great majority of patients with mild and/or periodic Cushing's syndrome suppress to overnight dexamethasone. Since patients with mild and/or periodic Cushing's syndrome are the patients in whom the identification of hypercortisolism is difficult, our results from this relatively small study suggest that this test should no longer be used to exclude these patients from further workup for Cushing's syndrome.


M.D., Ph.D. Theodore C. Friedman

Charles R. Drew University, Division of Endocrinology

1731 E. 120th St.

Los Angeles, CA 90059


Phone: 13106685197

Fax: 1 32 35 63 93 24

Email: tefriedm@cdrewu.edu

(electronic reprints will be sent by e-mail)