Test Details: This test is performed when overproduction of cortisol is suspected. The low-dose test can help differentiate healthy people from those who produce too much cortisol. The high-dose test can help determine if the abnormality is in the pituitary gland (Cushing's Disease). People with pituitary glands which produce too much ACTH will have an abnormal response to the low-dose test, but a normal response to the high dose.