Test Details: This test measures the level of free metanephrines in the blood. The test proves helpful to diagnose or rule out a rare tumor of the adrenal gland called a pheochromocytoma or a other rare tumor paraganglioma. These tumors are known to produce excess hormones called catecholamines, which are broken down to metanephrines. Testing also may be used when a tumor has been treated or removed to monitor for recurrence of the disease.