The inferior petrosal sinus sampling test, an elevated central ACTH concentration compared to a peripheral value (from arm veins) indicates pituitary dependent Cushing's disease. The test involves a microcatheter being advanced through initially the femoral vein and eventually into the inferior petrosal sinuses which lie along the internal aspect of the skull base which drain blood from the pituitary gland.

Metyrapone is an inhibitor of 11 beta hydroxylase, inhibiting the conversion of 11 deoxycortisol to cortisol, and can be used as treatment in Cushing’s syndrome.