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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.

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