During initial evaluation for pheochromocytoma, which test is used to screen for catecholamine metabolites?

• A. Serum cortisol
• B. Plasma or urine metanephrines
• C. Calcium
• D. TSH

Answer: (B)

Screening for pheochromocytoma relies on detecting products of catecholamine breakdown because the tumor’s output can be episodic. Metanephrines are formed from catecholamines inside tumor cells and are produced continuously, so their levels stay elevated more reliably than the parent catecholamines themselves. This makes measuring plasma free metanephrines or urinary fractionated metanephrines a highly sensitive and preferred initial screen for catecholamine activity from a pheochromocytoma.

The other tests listed don’t assess catecholamine metabolism: serum cortisol evaluates the adrenals’ cortisol axis, calcium relates to parathyroid and bone metabolism, and TSH assesses thyroid function.