For metanephrine testing to screen pheochromocytoma, which result is preferred?

• A. 24-hour metanephrine
• B. VMA
• C. Plasma catecholamines
• D. Serum adrenaline

Answer: (A)

Measuring metanephrines over a 24-hour period is preferred because metanephrines are produced continuously by catecholamine metabolism and are less affected by episodic release, stress, or day-to-day fluctuations. This makes 24-hour urinary metanephrines (or plasma free metanephrines) more sensitive and reliable for detecting pheochromocytoma than measuring VMA, plasma catecholamines, or serum adrenaline alone. VMA reflects downstream excretion and can be normal despite a tumor; plasma catecholamines and serum adrenaline are highly variable and can be normal between episodes, so they’re less dependable for screening.