Comparison of the Dexamethasone-Suppressed Corticotropin-Releasing Hormone Test and Low-Dose Dexamethasone Suppression Test in the Diagnosis of Cushing’s Syndrome
Open Access
- 1 July 2006
- journal article
- research article
- Published by The Endocrine Society in Journal of Clinical Endocrinology & Metabolism
- Vol. 91 (7), 2582-2586
- https://doi.org/10.1210/jc.2005-2143
Abstract
Context: The low-dose dexamethasone suppression test (LDDST) is widely used in confirming a diagnosis of Cushing’s syndrome. CRH administration at the end of an LDDST has been reported to improve the diagnostic accuracy of this test. Objective: Our objective was to assess whether CRH administration after a standard LDDST (LDDST-CRH test) improves diagnostic accuracy in Cushing’s syndrome. Design, Setting, and Participants: Thirty-six individuals with a clinical suspicion of Cushing’s syndrome each completed a standard LDDST and an LDDST-CRH test at Hammersmith Hospitals NHS Trust, London. The LDDST involved administration of 0.5 mg oral dexamethasone given 6-hourly for 48 h. Serum cortisol was measured 6 h after the last dose of dexamethasone, with a value of 50 nmol/liter or below excluding Cushing’s syndrome. Immediately after this, the LDDST-CRH test commenced with administration of a ninth dose of 0.5 mg dexamethasone. Exactly 2 h later, 100 μg human-sequence CRH was administered. Serum cortisol was measured 15 min after the CRH injection, with a value of less than 38 nmol/liter also excluding Cushing’s syndrome. Main Outcome Measure: Diagnosis or exclusion of Cushing’s syndrome was the main outcome measure. Results: Twelve subjects were diagnosed with Cushing’s syndrome (eight Cushing’s disease and four primary adrenal). The sensitivity of the LDDST in diagnosing Cushing’s syndrome was 100%, with a specificity of 88%. In contrast, although the sensitivity of the LDDST-CRH test was also 100%, specificity was reduced at 67%. These results give a positive predictive value of 80% for the LDDST and 60% for the LDDST-CRH test. Conclusion: This small study suggests that the addition of CRH to the LDDST does not improve the diagnostic accuracy of the standard LDDST in Cushing’s syndrome.Keywords
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