Basics: Testing: Dex Tests

Dexamethasone suppression test measures whether adrenocorticotrophic hormone (ACTH) secretion by the pituitary can be suppressed.

How the Test is Performed

During this test, you will receive dexamethasone. This is a strong man-made (synthetic) glucocorticoid medicine. Afterward, your blood is drawn so that the cortisol level in your blood can be measured.

There are two different types of dexamethasone suppression tests: low dose and high dose. Each type can either be done in an overnight (common) or standard (3-day) method (rare). There are different processes that may be used for either test. Examples of these are described below.

Common:

  • Low-dose overnight — You will get 1 milligram (mg) of dexamethasone at 11 p.m., and a health care provider will draw your blood the next morning at 8 a.m. for a cortisol measurement.
  • High-dose overnight — The 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 the next morning at 8 a.m. for a cortisol measurement.

Rare:

  • Standard low-dose — 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.
  • Standard high-dose — 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.

Read and follow the instructions carefully. The most common cause of an abnormal test result is when instructions are not followed.

How to Prepare for the Test

The provider may tell you to stop taking certain medicines that can affect the test, including:

  • Antibiotics
  • Anti-seizure drugs
  • Medicines that contain corticosteroids, such as hydrocortisone, prednisone
  • Estrogen
  • Oral birth control (contraceptives)
  • Water pills (diuretics)

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

This test is done when the 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 ACTH. The high-dose test can help determine whether the problem is in the pituitary gland (Cushing disease) or from a different site in the body (ectopic).

Dexamethasone is a man-made (synthetic) steroid that binds to the same receptor as cortisol. Dexamethasone reduces ACTH release in normal people. Therefore, taking dexamethasone should reduce ACTH level and lead to a decreased cortisol level.

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 Results

Cortisol level should decrease after you receive dexamethasone.

Low dose:

  • Overnight — 8 a.m. plasma cortisol lower than 1.8 micrograms per deciliter (mcg/dL) or 50 nanomoles per liter (nmol/L)
  • Standard — Urinary free cortisol on day 3 lower than 10 micrograms per day (mcg/day) or 280 nmol/L

High dose:

  • Overnight — greater than 50% reduction in plasma cortisol
  • Standard — greater than 90% reduction in urinary free cortisol

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:

The high-dose test can help tell a pituitary cause (Cushing 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 decrease in blood cortisol
  • ACTH level — low
  • In most cases, the high-dose test is not needed

Ectopic Cushing syndrome:

  • Low-dose test — no decrease in blood cortisol
  • ACTH level — high
  • High-dose test — no decrease in blood cortisol

Cushing syndrome caused by a pituitary tumor (Cushing disease)

  • Low-dose test — no decrease in blood cortisol
  • High-dose test — expected decrease in blood cortisol

False test results can occur due to many reasons, including different medicines, obesity, depression, and stress. False results are more common in women than men.

Most often, the dexamethasone level in the blood is measured in the morning along with the cortisol level. For the test result to be considered accurate, the dexamethasone level should be higher than 200 nanograms per deciliter (ng/dL) or 4.5 nanomoles per liter (nmol/L). Dexamethasone levels that are lower can cause a false-positive test result.

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another, and from one side of the body to the other. Taking blood 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 lightheaded
  • Multiple punctures to locate veins
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

Alternative Names

DST; ACTH suppression test; Cortisol suppression test

References

Chernecky CC, Berger BJ. Dexamethasone suppression test – diagnostic. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:437-438.

Guber HA, Oprea M, Russell YX. Evaluation of endocrine function. In: McPherson RA, Pincus MR, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 24th ed. St Louis, MO: Elsevier; 2022:chap 25.

Newell-Price JDC, Auchus RJ. The adrenal cortex. In: Melmed S, Auchus RJ, Goldfine AB, Koenig RJ, Rosen CJ, eds. Williams Textbook of Endocrinology. 14th ed. Philadelphia, PA: Elsevier; 2020:chap 15.

Review Date 5/13/2021

Updated by: Brent Wisse, MD, Board Certified in Metabolism/Endocrinology, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

From https://medlineplus.gov/ency/article/003694.htm

⁉️ Would *YOU* Do This?

I remember someone on the House TV series trying a stunt like this on the episode titled Deception.

At a betting parlor where House happens to be, a woman collapses and House makes sure she gets to the hospital. He thinks she has Cushing’s syndrome while Cameron starts to think she has Münchausen syndrome, a syndrome at which the patient creates the symptoms of a disease, guaranteeing them attention and sympathy.

Rare Case of Woman Manipulating Saliva Tests to Support Cushing’s Diagnosis

Late-night measures of cortisol levels in saliva may not be all that helpful in diagnosing Cushing’s syndrome, a group of physicians discovered upon learning that a difficult to diagnose patient had manipulated the samples.

Although this behavior is extremely rare, the research team from the University of Calgary in Canada, argued that — when a diagnosis becomes difficult — it may be advisable to confirm suspicions using another and more reliable method that can distinguish natural from synthetic glucocorticoids.

The study, Factitious ACTH- dependent, apparent hypercortisolism: the problem with late night salivary cortisol measurements collected at home,” was published in the journal Clinical Endocrinology.

The case report described a woman who was admitted to a specialist clinic after two endocrinologists had failed to diagnose what they suspected was cyclic Cushing’s syndrome.

The woman had complained of fatigue and weight gain over the past four years despite weight loss banding surgery, and declined taking steroid medications. The examination did not reveal particular Cushing’s symptoms.

Physicians started an investigation, including overnight dexamethasone suppression tests and late-night salivary cortisol tests, which indicate increased levels of cortisol likely caused by abnormal functioning of the ACTH hormone.

Imaging did not show any suspected lesions in the pituitary and adrenal gland, and all further examinations did not reveal any disease changes that might have contributed to the increased cortisol.

The woman was put on a dopamine agonist. This treatment triggered a loss of eight kilograms (almost 18 lbs) over six months, and the woman said she was satisfied with it. But two late-night cortisol measurement showed continuing high cortisol levels.

When the clinic started using a new type of analysis to measure cortisol, however, findings changed. The new test, which was more sensitive, indicated massively higher doses of cortisol in re-analyzed saliva samples compared to the older results.

The new test could detect synthetic glucosteroids, but could not indicate if synthetic steroids were responsible for the higher levels seen in the retest. So the team used a method called liquid chromatography-tandem mass spectrometry. This technique can identify specific molecules, and revealed that the women had manipulated the samples using prednisone.

The woman’s physician also paid a surprise visit to collect a new saliva sample, which turned out to have normal cortisol levels.

The woman neither denied or confirmed manipulating the samples. And the team was contacted two months later by her new physician, requesting confirmation of her Cushing’s syndrome and details on her case.

The researchers believed the woman most likely has what is known as Munchausen’s syndrome, a mental illness that leads patients to feign physical disease. A 1995 report by the National Institutes of Health showed that 0.7 percent of all people investigated for too high cortisol had this syndrome.

Despite the rarity of this case, the team argued that chemical analysis is a valuable tool for both determining sample manipulation in difficult Cushing’s syndrome cases, or a different potential problem.

They also cautioned against putting too much trust in very elevated late-night cortisol, particularly when the symptoms do not match the cortisol increase.

From https://cushingsdiseasenews.com/2017/10/05/rare-case-of-woman-manipulating-late-night-saliva-cortisol-tests-to-get-cushings-diagnosis/