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Dexamethasone suppression test interpretation — SCE Endocrinology MCQ

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ModerateEndocrine emergencies/dynamic testsDexamethasone suppression test interpretationSCE Endocrinology

A 47-year-old woman with possible Cushing's syndrome has 1 mg overnight dexamethasone suppression test. 09:00 cortisol is 28 nmol/L after dexamethasone. What is the most likely interpretation?

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Correct answer: E — Cushing's syndrome is unlikely on this test

Suppression of cortisol after dexamethasone makes endogenous Cushing's syndrome unlikely, assuming dexamethasone was taken and there is no assay issue. False positives can occur with oestrogens, enzyme inducers or non-adherence. Clinical suspicion may still justify alternative testing.

Reference: Endocrine Society Cushing's Syndrome Guideline