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
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 to 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.
How It Feels
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
Risks of a blood test
There is very little chance
of a problem from having blood sample taken from a vein.
You may get a small bruise at the site. You
can lower the chance of bruising by keeping pressure on the site for several
In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.
Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.
Bruising may be more
likely in people with high ACTH and cortisol levels.
The overnight dexamethasone suppression
test involves taking a dose of a
corticosteroid medicine called dexamethasone to see
how it affects the level of a hormone called
cortisol in the blood. This test screens for
Cushing's syndrome, a condition in which excess
amounts of cortisol are being produced by the adrenal glands. Test results are
usually available in a few days.
An abnormal test result may mean that
further testing is needed to identify Cushing's syndrome. Likewise, a normal
test result means that you do not have Cushing's syndrome. Cushing's
syndrome can be hard to diagnose, so an
endocrinologist should be consulted if test results
are uncertain or if the test results do not help explain your symptoms.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Cortisol level is less than 5
micrograms per deciliter (mcg/dL) or less than 138
nanomoles per liter (nmol/L).
High cortisol levels may be caused
problems, such as a heart attack or
heart failure, fever, poor diet, an overactive
thyroid gland (hyperthyroidism), depression,
anorexia nervosa, uncontrolled
diabetes, or alcoholism.
Cancers that make
ACTH, such as lung cancer.
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
Pregnancy or extreme
Severe weight loss, dehydration, or acute alcohol
take medicines, such as barbiturates, phenytoin (Dilantin), birth control
pills, aspirin, morphine, methadone, lithium, monoamine oxidase inhibitors
(MAOIs), spironolactone (Aldactone), or
Some people may quickly process (metabolize) the
dose of dexamethasone. In these people, cortisol levels will not drop unless a
higher dose of the medicine is given.
What To Think About
doctors think that a 24-hour urine free cortisol test is more accurate than an
overnight dexamethasone suppression test. Like an overnight dexamethasone
suppression test, a 24-hour urine free cortisol test is used to look for
Cushing's syndrome. For more information, see the topic Cortisol in Urine.
How this information was developed to help you make better health decisions.