Method for differentially diagnosing acth-dependent cushing's syndrome

A method of obtaining a measurement indicative of differential diagnosis of adrenocorticotropic hormone (ACTH)-dependent Cushing's syndrome in a patient where the differential diagnosis is between ectopic ACTH syndrome and Cushing's disease, the method comprising the steps of:

• selecting a patient having Cushing's syndrome, said patient having hypercortisolemia and an elevated ACTH level;
• determining the ACTH concentration ratio from said patient, where the patient has been administered a dose of a glucocorticoid receptor antagonist (GRA) at least two hours prior to the removal of venous samples, wherein said GRA dose is at least 300 milligrams (mg) and is no greater than 1500 mg of said GRA;
• wherein the ACTH concentration ratio is derived from the ACTH concentrations in a blood sample obtained from either the left or right inferior petrosal venous sinus of the patient and from a blood sample obtained from a peripheral vein of the patient;
• and
• wherein an ACTH concentration ratio of greater than 3 for the ACTH concentration from the inferior venous sinus blood sample over the periphery venous sinus blood sample is indicative of Cushing's disease.