Suspected Cushing's syndrome

Excludes Cushing's syndrome

Adrenal tumor

Ectopic ACTH Syndrome

Cushing disease

ACTH undetectable
No suppression

ACTH elevated
No suppression

ACTH normal to elevated
Dexamethasone suppression of Serum cortisol to 50% of baseline

24 hr Urinary free cortisol (UFC)
OR
Low-dose dexamethasone suppression test

Abnormal

Normal

Plasma ACTH and High-dose dexamethasone suppression test

ACTH undetectable

ACTH elevated

ACTH normal to elevated