Episode 6: How to Perform the Overnight Dexamethasone Suppression Test: A Step-by-Step Guide
A panelist discusses how the dexamethasone suppression test (DST) serves as a simple, cost-effective screening tool for cortisol excess, with proper timing and interpretation of both cortisol and dexamethasone levels being essential for accurate diagnosis and guiding further evaluation.
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 a simple, cost-effective, and reliable method for screening cortisol excess. The process begins with a clinician prescribing a 1-mg dexamethasone tablet, which the patient picks up from the pharmacy and takes at 11 PM. Timing is important to ensure the accuracy of the test. The following morning, precisely 9 hours after ingestion—typically around 8 AM—the patient visits the laboratory for bloodwork to measure both serum cortisol and dexamethasone levels.
For the results to be considered valid, the serum cortisol level must be assessed in conjunction with the dexamethasone level. If the cortisol level is below 1.8 μg/dL and the dexamethasone level is above 140 ng/dL, it indicates that cortisol suppression has occurred appropriately, making hypercortisolism unlikely. This outcome suggests the body responded correctly to the dexamethasone, simulating a healthy feedback loop within the hypothalamic-pituitary-adrenal axis.
However, if the cortisol level remains above 1.8 μg/dL despite a sufficient dexamethasone level, the test result is considered positive and warrants further evaluation. In such cases, the patient may have autonomous cortisol production, which should be investigated with additional diagnostic steps. If a clinician still strongly suspects hypercortisolism despite a normal test result, they may choose to repeat the DST or pursue a different type of cortisol assessment. This flexibility allows clinicians to tailor the diagnostic approach to individual patient presentations and ensures more accurate detection of cortisol abnormalities.
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