Is a Dexamethasone Suppression Test?
A dexamethasone suppression test is primarily used to help
syndrome. Cushing’s syndrome indicates that you have an abnormally high
level of cortisol. Cortisol is
a steroid hormone produced by the body during high levels of stress.
the Test Addresses
A dexamethasone suppression test measures how your cortisol
levels are affected by taking dexamethasone. Dexamethasone is a manmade corticosteroid similar to one
produced naturally by your adrenal glands. It’s prescribed to replace the natural chemical if your body isn’t
producing enough of it. It may also be prescribed as an anti-inflammatory agent
that’s used to treat arthritis and various blood, kidney, and eye disorders.
Your adrenal glands are
located on top of your kidneys. In addition to producing cortisol, they produce
steroid hormones such as:
- androgens, which are male sex hormones
The test is also used to determine how well the adrenal glands
respond to adrenocorticotropic hormone (ACTH). ACTH is a hormone produced by the brain’s pituitary gland. It
has a number of functions, including the production of corticosteroids. Too
much ACTH can cause Cushing’s syndrome. In a healthy person, as the pituitary
glands make less ACTH, the adrenal glands make less cortisol. Dexamethasone
should decrease the amount of ACTH, which should then cause the amount of cortisol
If you’re currently taking the corticosteroid medicine
dexamethasone, your doctor may recommend a dexamethasone suppression test to
determine how it’s affecting cortisol levels in your blood.
Dexamethasone relieves inflammation related to arthritis and severe
allergies, among other conditions. When you take dexamethasone, which is very
similar to cortisol, it should decrease the amount of ACTH released into your
blood. If your cortisol level is high after taking a dose of dexamethasone,
this is a sign of an abnormal condition.
for the Test
Before the test, your doctor will tell you to stop taking certain
prescription medications that may affect the results. These include:
- birth control pills
- phenytoin, which is used to treat seizures
which is used to treat congestive cirrhosis, ascites, or kidney problems
which is an antibiotic
Is the Test Administered?
Two variations of the dexamethasone suppression test are the
low-dose test and the high-dose test. Both forms of the test can be done
overnight or over the course of a three-day period. The standard test for both
is the test that spans three days. During both forms of the test, your doctor
will give you a certain amount of dexamethasone and will later measure your
levels of cortisol. A blood sample is also needed.
Blood will be drawn from a vein in the inside of your lower arm
or the back of your hand. First, your doctor will swab the site with
antiseptic. They may wrap an elastic band around the top of your arm to cause
the vein to swell with blood, making it more visible. Your doctor will then
insert a fine needle into the vein and collect a blood sample into a tube
attached to the needle. The band is removed and gauze is applied to the site to
prevent further bleeding.
Low-Dose Overnight Test
- Your doctor will give you 1 milligram of
dexamethasone at 11 p.m.
- They’ll draw a blood sample at 8 a.m. the
following morning to test your cortisol levels.
Standard Low-Dose Test
- You’ll collect urine samples over three days and store them in 24-hour collection bottles.
- On the second day, your doctor will give you 0.5 milligrams of oral dexamethasone every six hours for 48 hours.
High-Dose Overnight Test
- Your doctor will measure your cortisol levels on the morning of the test.
- You’ll be given 8 milligrams of dexamethasone at 11 p.m.
- Your doctor will take a blood sample at 8 a.m. to measure your cortisol levels.
Standard High-Dose Test
- You’ll collect samples of urine over three days and store them in 24-hour containers.
- On the second day, your doctor will give you 2 milligrams of oral dexamethasone every 6 hours for 48 hours.
An abnormal low-dose test result may indicate that you’re
suffering from an excessive release of cortisol. This is known as Cushing’s
syndrome. This disorder could be caused by an adrenal tumor, a pituitary tumor,
or a tumor elsewhere in your body that’s producing ACTH. The results of the
high-dose test can help isolate the cause of Cushing’s syndrome.
High cortisol levels may also be caused by a number of other
conditions such as:
- a heart attack
- heart failure
- a poor diet
- an overactive thyroid gland
- anorexia nervosa
- untreated diabetes
Are the Risks of the Test?
As with any blood draw, there’s a minimal risk of minor bruising
at the needle site. In rare cases, the vein may become swollen after blood is
drawn. This condition, known as phlebitis,
can be treated with a warm compress several times a day. Ongoing bleeding could
be a problem if you suffer from a bleeding disorder or you’re taking blood
thinners such as warfarin
(Coumadin) or aspirin.
up After the Test
Even with an abnormally high result, your doctor may recommend
further tests to diagnose Cushing’s syndrome. If this disorder is diagnosed,
you’ll be given appropriate medications to control your high cortisol levels.
If cancer is causing your high cortisol levels, your doctor will
recommend further tests to determine the type of cancer and the appropriate treatment.
If your high cortisol levels are caused by other disorders, your
doctor may recommend another course of treatment.