Test Details: Dexamethasone suppression test measures the response of the adrenal glands to Adrenocorticotropic hormone (ACTH). Dexamethasone is given and levels of cortisol are measured. The secretion of ACTH from the pituitary gland is normally regulated by the level of cortisol in the blood plasma. ACTH stimulates the adrenal cortex to produce cortisol. This test is done to help diagnose Cushing syndrome and identify the cause. The low-dose test can help tell whether your body is producing excess of ACTH.