What is the first clinical test indicated for diagnosing pheochromocytoma?

• A. CT scan
• B. Ultrasound
• C. Urine metanephrines test
• D. Blood test

Answer: (C)

The first clinical test indicated for diagnosing pheochromocytoma is the urine metanephrines test. Pheochromocytoma is a tumor of the adrenal gland that secretes catecholamines, leading to hypertension and other symptoms. The urine metanephrines test specifically measures the levels of metanephrine and normetanephrine, which are metabolites of catecholamines. Elevated levels in the urine are a strong indicator of pheochromocytoma.

When it comes to initial testing, assessing catecholamine metabolites is preferred because it provides a high sensitivity for detecting the presence of this tumor. While imaging studies such as CT scans and ultrasounds may eventually be used to locate the tumor once biochemical evidence is present, they are not first-line tests for diagnosis. Blood tests measuring plasma free metanephrines can also be helpful, but the urine metanephrines test remains the most widely used initial diagnostic tool due to its practicality and sensitivity.