dexamethasone suppression test checks to see how taking a
corticosteroid medicine (called dexamethasone) changes
the levels of the hormone
cortisol in the blood. This test checks for a
condition in which large amounts of cortisol are produced by the adrenal glands
Normally, when the pituitary gland make less
adrenocorticotropic hormone (ACTH), the
adrenal glands make less cortisol. Dexamethasone, which is like cortisol, decreases the amount of
ACTH released by the pituitary gland, which in turn decreases the amount of
cortisol released by the adrenal glands.
After taking a dose of
dexamethasone, cortisol levels often stay abnormally high in people who have
Cushing's syndrome. Sometimes other conditions (such as major depression,
alcoholism, stress, obesity, kidney failure, pregnancy, or uncontrolled
diabetes) can keep cortisol levels from going down
after taking a dose of dexamethasone.
The night before the blood
test, you will take a pill containing dexamethasone. The next morning, the
cortisol level in your blood will be measured. If your cortisol level remains
high, Cushing's syndrome may be the cause.
test is sometimes done at the same time as the cortisol test.
Why It Is Done
An overnight dexamethasone suppression
test is done to check for a condition in which large amounts of cortisol are
produced by the adrenal glands (Cushing's syndrome).
How To Prepare
You will not be able to eat or drink
anything for 10 to 12 hours before the morning blood test.
medicines can change the results of this test. Be sure to tell your doctor
about all the nonprescription and prescription medicines you take. You may be
asked to stop taking some medicines (such as birth control pills, aspirin,
morphine, methadone, lithium, monoamine oxidase inhibitors [MAOIs], and
diuretics) for 24 to 48 hours before your blood is
Talk to your doctor about any concerns you have about
the need for the test, its risks, how it will be done, or what the results will
mean. To help you learn about this test and how important it is, fill out the
medical test information form(What is a PDF document?).
How It Is Done
The night before the test
(usually at 11:00 p.m.), you will swallow a pill containing 1 milligram (mg) of
dexamethasone. The next morning (usually at 8:00 a.m.), a health professional
will draw a sample of your blood. Take the pill with milk or an antacid to help
prevent an upset stomach or heartburn.
The health professional
drawing blood will:
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure on the site and then put on a
Sometimes a more extensive dexamethasone suppression test may be
done. For this test, you will take up to 8 dexamethasone pills over 2 days and
then the cortisol levels in your blood and urine will be measured.