Establish high cortisol: first check 24-hour urine cortisol or 1 mg overnight dexamethasone suppression test or salivary cortisol (night)
Establish if ACTH dependent: Next step is to check ACTH level. If ACTH level is suppressed, then the problem is Cushing syndrome, CT or MRI of adrenals should be done. If ACTH level is elevated, the patient has either Cushing’s disease (pituitary problem) or ectopic production of ACTH (like lung cancer)
If ACTH dependent (High ACTH): To distinguish between Cushing’s disease and ectopic production of ACTH, perform a high dexamethasone suppression test (8 mg).
Localize the Tumor: Adrenal CT/MRI (ACTH indpendent), Pituitary MRI (ACTH dependent), Neck, chest, abdomen CT (ACTH dependent from Ectopic ACTH)