LabMed

Elevated 24-Hour Urine Free Cortisol

Differential Diagnosis

Pituitary cause for Cushing syndrome

Adrenal cause for Cushing syndrome

Ectopic ACTH secretion as a cause for Cushing syndrome

One of many conditions that produce a high cortisol level wtihout manifestations of Cushing syndrome

Suggested Additional Lab Testing

Pituitary Cushing syndrome

  • No ACTH suppression and, therefore, no cortisol suppression in the dexamethasone suppression test

  • Plasma ACTH elevated or occasionally normal

Adrenal Cushing syndrome

  • No ACTH suppression with dexamethasone suppression

  • Low plasma ACTH

Ectopic ACTH secretion producing Cushing syndrome

  • No ACTH suppression in the dexamethasone suppression test

  • For ectopic ACTH-secreting tumors, ACTH elevated, often at higher levels than found in Cushing disease from a pituitary cause

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