Dexamethasone suppression test Health Article

Definition

Dexamethasone suppression test measures the response of the adrenal glands to ACTH.

Alternative Names

DST; ACTH suppression test; Cortisol suppression test

How the test is performed

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.

• Low-dose overnight method -- you will get 1 mg of dexamethasone at 11 p.m., and a health care provider will draw your blood at 8 a.m. for a cortisol measurement.
• Standard low-dose method -- urine is collected over 3 days (stored in 24-hour collection containers) to measure cortisol. On day 2, you will get a low dose (0.5 mg) of dexamethasone by mouth every 6 hours for 48 hours.
• High-dose overnight method -- the health care provider will measure your cortisol on the morning of the test. Then you will receive 8 mg of dexamethasone at 11 p.m. Your blood is drawn at 8 a.m. for a cortisol measurement.
• Standard high-dose test -- urine is collected over 3 days (stored in 24-hour collection containers) for measurement of cortisol. On day 2, you will receive a high dose (2 mg) of dexamethasone by mouth every 6 hours for 48 hours.

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.

How to prepare for the test

The health care provider may advise you to stop taking drugs that may affect the test. Drugs that can affect test results include:

• Barbiturates
• Corticosteroids
• Estrogens
• Oral birth control (contraceptives)
• Phenytoin
• Spironolactone
• Tetracyclines