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 pinch.

Risks

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 minutes.
• 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.

Results

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 2 to 3 days.

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.

Normal

High values

High cortisol levels may be caused by:

• Cushing's syndrome.
• Other health 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 obesity.
• Severe weight loss, dehydration, or acute alcohol withdrawal.
• Severe injury.
• Diabetes.
• You take medicines, such as barbiturates, phenytoin (Dilantin), birth control pills, aspirin, morphine, methadone, lithium, monoamine oxidase inhibitors (MAOIs), spironolactone (Aldactone), and diuretics.

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.