What is the most conclusive test for the diagnosis of pheochromocytoma?

• A. CT scan
• B. MRI
• C. 24-hour urine sample
• D. Ultrasonography

Answer: (C)

Pheochromocytoma causes excess and episodic release of catecholamines, so the most reliable way to confirm the diagnosis is a biochemical test that proves this excess. Measuring metanephrines, stable metabolites of catecholamines, provides the highest diagnostic accuracy because they remain elevated even when a patient has intermittent secretion. A 24-hour urine collection for fractionated metanephrines and catecholamines captures the day-to-day production and offers strong sensitivity and specificity. Imaging studies like CT, MRI, or ultrasonography can show where a tumor might be, but they do not prove that the tumor is hormonally active, so they are not the definitive test for diagnosis.