Metanephrine [24h Urine] test measures the amount of metanephrine in urine collected over 24 hours. Metanephrine is a breakdown product of epinephrine and norepinephrine, two hormones produced by the adrenal glands. This test is used to diagnose pheochromocytoma, a rare tumor of the adrenal gland that causes difficult-to-control high blood pressure. High levels of metanephrine in urine may be a sign of pheochromocytoma.