Metanephrine is primarily used in medical diagnostics to help detect and monitor pheochromocytoma, a rare tumor of the adrenal glands. It is measured in urine or blood tests to assess the levels of catecholamines, which are often elevated in patients with this condition. Accurate measurement of metanephrine aids in diagnosing the tumor and evaluating the effectiveness of treatment. Additionally, it is used to distinguish pheochromocytoma from other conditions with similar symptoms, such as anxiety or hypertension. Regular monitoring of metanephrine levels is crucial for managing patients with suspected or confirmed adrenal tumors.