Dexamethasone suppression test measures the response of the adrenal glands to ACTH.
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.
The health care provider may advise you to stop taking drugs that may affect the test. Drugs that can affect test results include:
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.
This test is performed when the health care provider suspects that your body is producing too much cortisol. It is done to help diagnose Cushing syndrome and identify the cause.
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.
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.
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)
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:
DST; ACTH suppression test; Cortisol suppression test