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Alternative NamesDST; ACTH suppression test; Cortisol suppression test
Definition Return to top
Dexamethasone suppression test measures the response of the adrenal glands to ACTH.
How the Test is Performed Return to top
During this test, you will receive dexamethasone, and the health care provider will measure your cortisol levels.
There are two different types of dexamethasone suppression tests: the low-dose test and the high-dose test. Each type can either be done in an overnight or standard (3-day) way.
Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
How to Prepare for the Test Return to top
The health care provider may advise you to stop taking drugs that may affect the test. Drugs that can affect test results include:
How the Test Will Feel Return to top
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed Return to top
This test is performed when the health care provider suspects that your body is producing too much cortisol.
The low-dose test can help tell whether your body is producing too much cortisol. The high-dose test can help determine whether the problem is in the pituitary gland (Cushing's disease).
The level of cortisol in the blood normally regulates the release of ACTH from the pituitary gland. As blood cortisol levels increase, ACTH release decreases. As cortisol levels decrease, ACTH increases.
Dexamethasone is a human-made (synthetic) steroid that is similar to cortisol. It reduces ACTH release in normal people. Therefore, taking dexamethasone should reduce ACTH levels and lead to decreased cortisol levels.
If your pituitary gland produces too much ACTH, you will have an abnormal response to the low-dose test, but a normal response to the high-dose test.
Normal Results Return to top
Cortisol levels should decrease after you receive dexamethasone.
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 Return to top
An abnormal response to the low-dose test may mean that you have abnormal release of cortisol (Cushing syndrome). This could be due to:
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:
Cushing syndrome related to an ectopic ACTH-producing tumor:
Cushing syndrome caused by a pituitary tumor (Cushing's disease)
Risks Return to top
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
References Return to top
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.Update Date: 3/18/2008 Updated by: 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.