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Overnight Dexamethasone Suppression Test

Test Overview

The overnight dexamethasone suppression test checks to see how taking a steroid medicine called dexamethasone changes the levels of the hormone cortisol, Opens dialog in the blood. This test checks for a condition in which large amounts of cortisol are produced by the adrenal glands (Cushing's syndrome, Opens dialog).

Normally, when the pituitary gland, Opens dialog makes less adrenocorticotropic hormone (ACTH), Opens dialog, the adrenal glands, Opens dialog make less cortisol. Dexamethasone, which is like cortisol, lowers the amount of ACTH released by the pituitary gland. This in turn lowers the amount of cortisol released by the adrenal glands.

After a dose of dexamethasone, cortisol levels often stay very high in people who have Cushing's syndrome. Sometimes other conditions can keep cortisol levels high during this test. Examples include alcohol use disorder, Opens dialog, stress, obesity, kidney failure, pregnancy, and uncontrolled diabetes.

The night before the blood test, you will take a dexamethasone pill. The next morning, the cortisol level in your blood will be measured. If your cortisol level stays high, Cushing's syndrome may be the cause.

An ACTH test is sometimes done at the same time as the cortisol test.

Current as of: April 30, 2024

Author: Ignite Healthwise, LLC Staff

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All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.

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