Reasons, Preparation & Procedure For Conducting a ACTH Dexamethasone Suppression Test

Submitted on March 27, 2012

ACTH Dexamethasone Suppression Test

The ACTH dexamethasone suppression test is done to see the changes in the level of cortisol on the blood, after a person takes a corticosteroid medicine, which is known as dexamethasone. This is done when a person has a condition called Cushing's syndrome, where the adrenal glands produce a lot of cortisol.

Generally, a dose of dexamethasone, keeps the cortisol levels very high in people who have Cushing's syndrome. Other conditions like uncontrolled diabetes, pregnancy, kidney failure, obesity, stress, alcoholism and severe depression can stop the level of cortisol from dipping, after the patient has had dexamethasone.

Before the blood test, the person is given a desamethasone pill, and in the morning, the level of cortisol in the blood is measured. It could be Cushing's syndrome if the level of cortisol remains high. An ACTH test may be done along with this test too.

Why is the Test Done?

This test is done to check for Cushing's syndrome - a condition in which, the adrenal glands of the patient produces large amounts of cortisol.


Your physician will ask you to avoid eating or drinking for 10-12 hours before the blood test is carried out. Since medicines can change the results, you must inform your doctor of any medicines that you have taken recently.


The previous night, you will be asked to swallow a dexamethasone pill, maybe with a glass of milk to prevent heartburn. In the morning, a blood sample will be taken by your health professional.

Risks Involved

There are hardly any risks to getting your blood drawn. At the most, that area might feel sore and there might be a small bruise. You can use a warm compress to get relief.

What Affects the Test?

You may not be suitable for the test if you have diabetes, severe injury, acute alcohol withdrawal, dehydration, severe weight loss, obesity or if you are pregnant.

Interpretation of Test Results

This particular test can determine if a person has Cushing's syndrome. If the test results are abnormal, the patient might need further tests to confirm and identify Cushing's syndrome. A normal test means that the person does not have Cushing's syndrome.

In some cases doctors may have to do extensive dexamethasone suppression tests, in which the patient will be asked to take about eight pills in two days. Then the level of cortisol will be determined by urine and blood tests