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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: Adrenal tumor that produces cortisol Pituitary tumor that produces ACTH Tumor in the body that produces ACTH (ectopic Cushing syndrome) 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
An assessment of free cortisol after a dexamethasone suppression test could add value to the diagnostic workup of hypercortisolism, which can be plagued by false-positive results, according to data from a cross-sectional study. A 1 mg dexamethasone suppression test (DST) is a standard of care endocrine test for evaluation of adrenal masses and for patients suspected to have endogenous Cushing’s syndrome. Interpretation of a DST is affected by dexamethasone absorption and metabolism; several studies suggest a rate of 6% to 20% of false-positive results because of inadequate dexamethasone concentrations or differences in the proportion of cortisol bound to corticosteroid-binding globulin affecting total cortisol concentrations. Source: Adobe Stock “As the prevalence of adrenal adenomas is around 5% to 7% in adults undergoing an abdominal CT scan, it is important to accurately interpret the DST,” Irina Bancos, MD, associate professor in the division of endocrinology at Mayo Clinic in Rochester, Minnesota, told Healio. “False-positive DST results are common, around 15% of cases, and as such, additional or second-line testing is often considered by physicians, including measuring dexamethasone concentrations at the time of the DST, repeating DST or performing DST with a higher dose of dexamethasone. We hypothesized that free cortisol measurements during the DST will be more accurate than total cortisol measurements, especially among those treated with oral contraceptive therapy.” Diverse cohort analyzed Bancos and colleagues analyzed data from adult volunteers without adrenal disorders (n = 168; 47 women on oral contraceptive therapy) and participants undergoing evaluation for hypercortisolism (n = 196; 16 women on oral contraceptives). The researchers assessed levels of post-DST dexamethasone and free cortisol, using mass spectrometry, and total cortisol, via immunoassay. The primary outcome was a reference range for post-DST free cortisol levels and the diagnostic accuracy of post-DST total cortisol level. Irina Bancos “A group that presents a particular challenge are women treated with oral estrogen,” Bancos told Healio. “In these cases, total cortisol increases due to estrogen-stimulated cortisol-binding globulin production, potentially leading to false-positive DST results. We intentionally designed our study to include a large reference group of women treated with oral contraceptive therapy allowing us to develop normal ranges of post-DST total and free cortisol, and then apply these cutoffs to the clinical practice.” Researchers observed adequate dexamethasone concentrations ( 0.1 µg/dL) in 97.6% of healthy volunteers and in 96.3% of patients. Among women volunteers taking oral contraceptives, 25.5% had an abnormal post-DST total cortisol measurement, defined as a cortisol level of at least 1.8 µg/dL. Among healthy volunteers, the upper post-DST free cortisol range was 48 ng/dL in men and women not taking oral contraceptives, and 79 ng/dL for women taking oral contraceptives. Compared with post-DST free cortisol, diagnostic accuracy of post-DST total cortisol level was 87.3% (95% CI, 81.7-91.7). All false-positive results occurred among patients with a post-DST cortisol level between 1.8 µg/dL and 5 µg/dL, according to researchers. Oral contraceptive use was the only factor associated with false-positive results (21.1% vs. 4.9%; P = .02). Findings challenge guidelines Natalia Genere “We were surprised by several findings of our study,” Natalia Genere, MD, instructor in medicine in the division of endocrinology, metabolism and lipid research at Washington University School of Medicine in St. Louis, told Healio. “First, we saw that with a standardized patient instruction on DST, we found that optimal dexamethasone concentrations were reached in a higher proportion of patients than previously reported (97%), suggesting that rapid metabolism or poor absorption of dexamethasone may play a lower role in the rate of false positives. Second, we found that measurements of post-DST total cortisol in women taking oral contraceptive therapy accurately excluded [mild autonomous cortisol secretion] in three-quarters of patients, suggesting discontinuation of oral contraceptives, as suggested in prior guidelines, may not be routinely necessary.” Genere said post-DST free cortisol performed “much better” than total cortisol among women treated with oral estrogen. Stepwise approach recommended Based on the findings, the authors suggested a sequential approach to dexamethasone suppression in clinical practice. “We recommend a stepwise approach to enhance DST interpretation, with the addition of dexamethasone concentration and/or free cortisol in cases of abnormal post-DST total cortisol,” Bancos said. “We found dexamethasone concentrations are particularly helpful when post-DST total cortisol is at least 5 µg/dL and free cortisol is helpful in a patient with optimal dexamethasone concentrations and a post-DST total cortisol between 1.8 µg/dL and 5 µg/dL. We believe that DST with free cortisol is a useful addition to the repertoire of available testing for [mild autonomous cortisol secretion], and that its use reduces need for repetitive assessments and patient burden of care, especially in women treated with oral contraceptive therapy.” PERSPECTIVE BACK TO TOP Ricardo Correa, MD, EsD, FACE, FACP, CMQ In the evaluation of endogenous Cushing’s disease, the guideline algorithm recommends two of three positive tests — 24-hour free urine cortisol, late midnight salivary cortisol level and 1 mg dexamethasone suppression test, or DST — for diagnosing hypercortisolism. Of those tests, the most accurate to detect adrenal secretion of cortisol when a patient may have an adrenal incidentaloma is the 1 mg DST. The caveat with this specific test is that it is affected by dexamethasone absorption and metabolism and the proportion of cortisol bound to corticosteroid-binding globulin. Up to 20% of these tests report false-positive findings. This study by Genere and colleagues aimed to determine the normal range of free cortisol during the 1 mg DST. The researchers conducted a prospective, cross-sectional study that included volunteers without adrenal disorders and patients assessed for cortisol excess for clinical reasons. In the volunteer group, 168 volunteers were enrolled, including 47 women that were taking oral contraceptives. After excluding patients with inadequate dexamethasone levels and other outliers, the post-DST free cortisol maximum level was less than 48 ng/dL for men and women who were not taking oral contraceptive pills and less than 79 ng/dL for women taking oral contraceptive pills. In the patient group, 100% of post-DST free cortisol levels were above the upper limit of normal among those with a post-DST cortisol of at least 5 µg/dL; however, this was true for only 70.7% of those with post-DST cortisol between 1.8 µg/dL and 5 µg/dL. This study found that a post-DST free cortisol assessment is helpful in patients with a post-DST total cortisol between 1.8 µg/dL and 5 µg/dL, but was not beneficial for patients with a post-DST total cortisol of less than 1.8 µg/dL or more than 5 µg/dL. Performing free cortisol assessments in this subgroup will reduce the number of false positives. The authors recommend performing a 1 mg post-DST free cortisol analysis for this subgroup; the levels to confirm cortisol excess are at least 48 ng/dL in men and women not taking oral contraceptive pills and at least 79 ng/dL for women taking oral contraceptive pills. Furthermore, the study presents a stepwise approach algorithm that will be very useful for clinical practice. Ricardo Correa, MD, EsD, FACE, FACP, CMQ Endocrine Today Editorial Board Member Program Director of Endocrinology Fellowship and Director for Diversity University of Arizona College of Medicine-Phoenix Phoenix Veterans Affairs Medical Center Disclosures: Correa reports no relevant financial disclosures. From https://www.healio.com/news/endocrinology/20211117/free-cortisol-evaluation-useful-after-abnormal-dexamethasone-test