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Dexamethasone suppression test - Results

Alternative Names

DST; ACTH suppression test; Cortisol suppression test

Normal Values:

Cortisol levels should decrease after you receive dexamethasone.

Low dose:

  • Overnight: 8 a.m. plasma cortisol < 1.8 mcg/dl
  • Standard: Urinary free cortisol on day 3 < 10 mcg/day

High dose:

  • Overnight: > 50% reduction in plasma cortisol
  • Standard: > 90% reduction in urinary free cortisol

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean:

An abnormal response to the low-dose test may mean that you have abnormal release of cortisol (Cushing syndrome). This could be due to:

  • Adrenal tumor that produces cortisol
  • Pituitary tumor that produces ACTH
  • Tumor in the body that produces ACTH

The high-dose test can help tell a pituitary cause (Cushing's disease) from other causes.

Abnormal results vary based on the condition causing the problem.

Cushing syndrome caused by an adrenal tumor:

  • Low-dose test: no change
  • High-dose test: no change

Cushing syndrome related to an ectopic ACTH-producing tumor:

  • Low-dose test: no change
  • High-dose test: no change

Cushing syndrome caused by a pituitary tumor (Cushing's disease)

  • Low-dose test: no change
  • High-dose test: normal suppression
  • Reviewed last on: 3/18/2008
  • Elizabeth H. Holt, MD, PhD, Assistant Professor of Medicine, Section of Endocrinology and Metabolism, Yale University. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

References

Stewart PM. The adrenal cortex. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia, PA: Saunders Elsevier; 2008: chap 14.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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