Dexamethasone suppression test

Alternative names:

ACTH suppression test; cortisol suppression test; DST

How the test is performed:

There are basically 2 ways to give the test: the rapid method and the 6-day method. In the rapid method, 1 mg of dexamethasone is given at 11 P.M., and the blood is drawn at 8 A.M. for a cortisol measurement (see venipuncture). If no decrease in the amount of cortisol is seen, the test is repeated with an 8-mg dose of dexamethasone.

In the 6-day method, urine is collected at 24-hour intervals over 6 days for measurement of cortisol or 17-OCHS. On day 3, a low dose (0.5 mg) of dexamethasone is given by mouth every 6 hours for 24-hours. On day 5, the procedure is repeated with a high dose (2.0 mg) of dexamethasone.

How to prepare for the test:

The health care provider may advise you to discontinue drugs that may affect the test. Drugs that can affect test results include barbiturates, estrogens, corticosteroids, oral contraceptives, phenytoin, spironolactone, and tetracyclines.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:

• infant test or procedure preparation (birth to 1 year)
• toddler test or procedure preparation (1 to 3 years)
• preschooler test or procedure preparation (3 to 6 years)
• schoolage test or procedure preparation (6 to 12 years)
• adolescent test or procedure preparation (12 to 18 years)

How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

This test is performed when adrenal disease is suspected; it can differentiate adrenal disease (altered response to ACTH) from pituitary disorders (altered production of ACTH).

The secretion of ACTH from the pituitary gland is normally regulated by the level of cortisol in the plasma. ACTH stimulates the adrenal cortex to produce cortisol. As plasma cortisol levels increase, ACTH secretion is suppressed, as cortisol levels decrease and ACTH increases. Dexamethasone is a synthetic steroid similar to cortisol, which suppresses ACTH secretion in normal people; giving dexamethasone should reduce ACTH levels resulting in decreased cortisol levels.