Overnight dexamethasone suppression test

This test is done to check for Cushing's syndrome. It is a condition in which large amounts of cortisol are produced by the adrenal glands.

The night before the test (usually at 11:00 p.m.), you will swallow a pill that contains 1 milligram (mg) of dexamethasone. Take the pill with milk or an antacid. This can help prevent an upset stomach or heartburn.

The next morning (usually at 8:00 a.m.), you will have a sample of your blood drawn. A health professional uses a needle to take a blood sample, usually from the arm.

Sometimes a more complete dexamethasone suppression test may be done. For this test, you will take up to 8 pills over 2 days. Then the cortisol levels in your blood and urine will be measured.

Many medicines can change the results of this test. You may be asked to stop taking some medicines for 24 to 48 hours before your blood is drawn.

Test results are usually ready in a few days.

An abnormal test result may mean that more tests are needed. A normal test result means that you do not have Cushing's syndrome. This syndrome can be hard to diagnose. So if the test results aren't clear or if they don't help explain your symptoms, you may be referred to see an endocrinologist.

Normal

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

High values

High cortisol levels may be caused by:

• Cushing's syndrome.
• Other health problems. Examples include heart attack or heart failure, fever, poor diet, an overactive thyroid gland (hyperthyroidism), depression, anorexia nervosa, uncontrolled diabetes, and alcohol use disorder.