Checking for Excess Cortisol
Dexamethasone Suppression Test (DST)
This resource explains why the DST test was ordered, how dexamethasone works, what to do the night before and morning of the test, which medicines or circumstances to discuss, and how to understand the results.
For Clinicians
This test checklist was developed for use as a clinical workflow and patient-communication tool. It can be incorporated into your pre-visit preparation and shared as a reference with patients.
For Patients
This checklist is designed to help you prepare for and understand a Dexamethasone Suppression Test (DST). It's not a substitute for your physician's guidance, but a tool to help you ask better questions and follow the process correctly.
Why Your Doctor Asked You to Have This Test
Your doctor ordered this test because your health history, symptoms, or imaging raised a question about whether your cortisol level may be higher than expected. The test checks whether your body can properly switch off cortisol production, which helps your care team confirm or rule out Cushing Syndrome, also called hypercortisolism.
1How your body controls cortisol
Cortisol is made by your adrenal glands. It helps you respond to stress and keeps blood sugar, blood pressure, immune function, and bone and muscle health in balance.
Cortisol follows a daily rhythm: it is usually higher in the morning to help you wake up and lower at night while you sleep. When cortisol is high enough, the pituitary gland lowers ACTH, a hormone that tells the adrenal glands to make cortisol. This helps the adrenal glands make less cortisol.
2What the test does
Dexamethasone acts like cortisol in the body. A small dose taken late at night should switch off ACTH, the messenger hormone from the pituitary gland, so cortisol is low by the next morning.
If your cortisol is still elevated the next morning, it suggests the off switch is not working the way it should. That is a reason to look further.
3Why this test may have been ordered for you
Doctors often check cortisol when someone has a condition that too much cortisol can cause or worsen, such as (but not limited to):
- High blood pressure that is hard to control
- Diabetes or high blood sugar that is hard to control
- Osteoporosis, especially if it is early or severe
- An adrenal nodule found on a CT or MRI scan done for another reason
- Recent weight gain around the abdomen and face, thin skin or easy bruising, muscle weakness, or mood changes
Being sent for this test does not mean your doctor expects to find a problem.
This is a screening test, and most people who take it have a normal result. If you are asked to repeat it, or to have a different test afterward, that is routine.
Plan ahead
Get ready for your test
Use the Test Plan Chart to schedule and keep track of your dexamethasone tablet and your blood-draw appointment. It also answers common questions about the DST.
