Overnight Dexamethasone Suppression Test
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.
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 a 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.