Episode 5: The Dexamethasone Suppression Test: A Clinician’s Guide to Cortisol Screening
A panelist discusses how the dexamethasone suppression test (DST), particularly the 1-mg overnight test and 2-day low-dose test, is used to screen for cortisol excess, with the 2-day test offering higher specificity and the choice of test depending on the clinical context and patient symptoms.
By
Pamela Kushner, MD
| Published on June 11, 2025
2 min read
The following is an AI-generated summary based on the video content above:
The DST is considered the most sensitive method for screening cortisol excess, with a sensitivity rate of up to 95%. This test measures how the adrenal glands respond to corticotropin, the hormone responsible for cortisol production. When cortisol levels are adequate, the body should suppress further production and the administration of dexamethasone in this test should lead to a decrease in cortisol. If cortisol levels remain elevated after the test, it suggests autonomous cortisol production, indicating a need for further investigation.
There are 2 common types of dexamethasone suppression tests used clinically: the 1-mg overnight test and the 2-day low-dose test. The 1-mg overnight test is the most commonly used. In this method, the patient takes dexamethasone at 11 PM and a cortisol level is measured the following morning at 8 AM. If the cortisol level exceeds 1.8 μg/dL, it indicates that cortisol suppression did not occur as expected. This test is relatively straightforward and efficient for screening. The 2-day test involves administering a lower dose of dexamethasone every 6 hours for 2 days, with cortisol levels measured after the final dose.
Although both tests are useful, the 2-day low-dose test offers superior specificity (97%) compared with the 1-mg overnight test (86%). This makes the 2-day test more reliable in confirming the diagnosis of cortisol excess. Both tests, however, are effective screening tools for detecting hypercortisolism and determining whether further diagnostic measures are necessary. Ultimately, choosing between the 2 tests depends on the clinical context and the patient’s specific symptoms.
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