Metanephrines are used to detect if you are suffering from Catecholamine secreting tumors such as Pheochromocytomas or Paragangliomas. Pheochromocytoma is a rare tumor arising from special cells in your adrenal gland. These patients develop high blood pressure with palpitations, severe headaches & sweating. Breakdown of Catecholamines produces Metanephrines which can be accurately measured in your blood. Your physician will order this test if there are symptoms of unstable or fluctuating high blood pressure, no response to blood pressure lowering drugs or presence of adrenal mass which is suspicious of Pheochromocytoma.