Comparison of the dexamethasone-suppressed corticotropin-releasing hormone test and low-dose dexamethasone suppression test in the diagnosis of Cushing's syndrome

J Clin Endocrinol Metab. 2006 Jul;91(7):2582-6. doi: 10.1210/jc.2005-2143. Epub 2006 May 2.


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 mug 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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cohort Studies
  • Corticotropin-Releasing Hormone* / administration & dosage
  • Cushing Syndrome / diagnosis*
  • Dexamethasone* / administration & dosage
  • Female
  • Humans
  • Hydrocortisone / blood
  • Male
  • Sensitivity and Specificity


  • Dexamethasone
  • Corticotropin-Releasing Hormone
  • Hydrocortisone