How is the overnight 1 mg DST performed?

Give 1 mg dexamethasone at 11 PM. Measure serum cortisol at 8 AM the next morning. Normal suppression: cortisol below 1.8 mcg/dL (50 nmol/L). Failure to suppress suggests hypercortisolism requiring further evaluation.

What are false positives in the overnight DST?

False positives (failure to suppress despite no Cushings) occur with: oral estrogens (increase CBG), anticonvulsants (accelerate dexamethasone metabolism), depression, anxiety, alcoholism, obesity, and physical stress/illness.

What are the three first-line tests for Cushing syndrome?

The three first-line tests recommended by the Endocrine Society are: 24-hour urinary free cortisol, late-night salivary cortisol (twice), and the low-dose dexamethasone suppression test. At least two abnormal results are required for diagnosis.

Dexamethasone Suppression Test Interpretation

Interpret overnight 1mg DST: normal cortisol below 1.8 mcg/dL excludes Cushings. Failure to suppress (above 1.8) requires further evaluation with 24h urinary cortisol or late-night salivary cortisol.

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Frequently Asked Questions

How is the overnight 1 mg DST performed?

What are false positives in the overnight DST?

What are the three first-line tests for Cushing syndrome?