Cushing syndrome — ABIM Board MCQ
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Correct answer: D — Obtain two late-night salivary cortisol measurements
The best answer is “Obtain two late-night salivary cortisol measurements”. Loss of the normal late-night cortisol nadir is a validated screening signal, and two salivary samples reduce biologic variability. Other accepted initial tests include repeated urine free cortisol or an overnight dexamethasone suppression test. Random cortisol is unreliable, and etiologic testing follows confirmation of hypercortisolism.
Reference: Endocrine Society Guideline: Diagnosis of Cushing Syndrome: https://www.endocrine.org/clinical-practice-guidelines/diagnosis-of-cushing-syndrome