Navigate Up

Heart Center - A-Z Index

#
J
Q
X
Z

Print This Page

Dexamethasone suppression test

Dexamethasone suppression test measures the response of the adrenal glands to ACTH .

Alternative Names

DST; ACTH suppression test; Cortisol suppression test

How the test is performed

During this test, you will receive dexamethasone, and the health care provider will measure your cortisol levels.

There are two different types of dexamethasone suppression tests: the low-dose test and the high-dose test. Each type can either be done in an overnight or standard (3-day) way.

  • Low-dose overnight method -- you will get 1 mg of dexamethasone at 11 p.m., and a health care provider will draw your blood at 8 a.m. for a cortisol measurement .
  • Standard low-dose method -- urine is collected over 3 days (stored in 24-hour collection containers) to measure cortisol. On day 2, you will get a low dose (0.5 mg) of dexamethasone by mouth every 6 hours for 48 hours.
  • High-dose overnight method -- the health care provider will measure your cortisol on the morning of the test. Then you will receive 8 mg of dexamethasone at 11 p.m. Your blood is drawn at 8 a.m. for a cortisol measurement.
  • Standard high-dose test -- urine is collected over 3 days (stored in 24-hour collection containers) for measurement of cortisol. On day 2, you will receive a high dose (2 mg) of dexamethasone by mouth every 6 hours for 48 hours.

A blood sample is needed. For information on how this is done, see: Venipuncture

How to prepare for the test

The health care provider may advise you to stop taking drugs that may affect the test. Drugs that can affect test results include:

  • Barbiturates
  • Corticosteroids
  • Estrogens
  • Oral birth control (contraceptives)
  • Phenytoin
  • Spironolactone
  • Tetracyclines

How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

This test is performed when the health care provider suspects that your body is producing too much cortisol. It is done to help diagnose Cushing syndrome and identify the cause.

The low-dose test can help tell whether your body is producing too much cortisol. The high-dose test can help determine whether the problem is in the pituitary gland (Cushing's disease ).

The level of cortisol in the blood normally regulates the release of ACTH from the pituitary gland. As blood cortisol levels increase, ACTH release decreases. As cortisol levels decrease, ACTH increases.

Dexamethasone is a human-made (synthetic) steroid that is similar to cortisol. It reduces ACTH release in normal people. Therefore, taking dexamethasone should reduce ACTH levels and lead to decreased cortisol levels.

If your pituitary gland produces too much ACTH, you will have an abnormal response to the low-dose test, but you can have a normal response to the high-dose test.

Normal Values

Cortisol levels should decrease after you receive dexamethasone.

Low dose:

  • Overnight: 8 a.m. plasma cortisol < 1.8 mcg/dl
  • Standard: Urinary free cortisol on day 3 < 10 mcg/day

High dose:

  • Overnight: > 50% reduction in plasma cortisol
  • Standard: > 90% reduction in urinary free cortisol

The examples above are common measurements for results for these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different specimens.Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

An abnormal response to the low-dose test may mean that you have abnormal release of cortisol (Cushing syndrome ). This could be due to:

  • Adrenal tumor that produces cortisol
  • Pituitary tumor that produces ACTH
  • Tumor in the body that produces ACTH

The high-dose test can help tell a pituitary cause (Cushing's disease) from other causes. An ACTH blood test may also help identify the cause of high cortisol.

Abnormal results vary based on the condition causing the problem.

Cushing syndrome caused by an adrenal tumor:

  • Low-dose test: no change
  • ACTH level: low
  • In most cases, the high-dose test is not needed

Cushing syndrome related to an ectopic ACTH-producing tumor:

  • Low-dose test: no change
  • ACTH level: high
  • High-dose test: no change

Cushing syndrome caused by a pituitary tumor (Cushing's disease)

  • Low-dose test: no change
  • High-dose test: normal suppression (however, some do not suppress, and another test is needed)

What the risks are

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

References

Stewart PM, Krone NP. The adrenal cortex. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Saunders Elsevier; 2011: chap 15.

Updated: 12/11/2011

Nancy J. Rennert, MD, Chief of Endocrinology & Diabetes, Norwalk Hospital, Associate Clinical Professor of Medicine, Yale University School of Medicine, New Haven, CT. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.


©  UPMC | Affiliated with the University of Pittsburgh Schools of the Health Sciences
Supplemental content provided by A.D.A.M. Health Solutions. All rights reserved.

For help in finding a doctor or health service that suits your needs, call the UPMC Referral Service at 412-647-UPMC (8762) or 1-800-533-UPMC (8762). Select option 1.

UPMC is an equal opportunity employer. UPMC policy prohibits discrimination or harassment on the basis of race, color, religion, ancestry, national origin, age, sex, genetics, sexual orientation, marital status, familial status, disability, veteran status, or any other legally protected group status. Further, UPMC will continue to support and promote equal employment opportunity, human dignity, and racial, ethnic, and cultural diversity. This policy applies to admissions, employment, and access to and treatment in UPMC programs and activities. This commitment is made by UPMC in accordance with federal, state, and/or local laws and regulations.

Medical information made available on UPMC.com is not intended to be used as a substitute for professional medical advice, diagnosis, or treatment. You should not rely entirely on this information for your health care needs. Ask your own doctor or health care provider any specific medical questions that you have. Further, UPMC.com is not a tool to be used in the case of an emergency. If an emergency arises, you should seek appropriate emergency medical services.

For UPMC Mercy Patients: As a Catholic hospital, UPMC Mercy abides by the Ethical and Religious Directives for Catholic Health Care Services, as determined by the United States Conference of Catholic Bishops. As such, UPMC Mercy neither endorses nor provides medical practices and/or procedures that contradict the moral teachings of the Roman Catholic Church.

© UPMC
Pittsburgh, PA, USA UPMC.com