Which laboratory test detects excessive catecholamine degradation products in the urine?

• A. Dexamethasone suppression
• B. Metanephrine and normetanephrine
• C. Creatinine clearance
• D. Schilling test

Answer: (B)

Measuring metanephrine and normetanephrine in urine detects excessive catecholamine degradation products. Catecholamines like epinephrine and norepinephrine are broken down into metanephrine and normetanephrine, which are then excreted in urine. In conditions such as pheochromocytoma, tumor-driven catecholamine excess leads to elevated levels of these metabolites, making urinary metanephrines a sensitive and specific test for abnormal catecholamine metabolism. This approach is often more reliable than measuring catecholamines themselves because metanephrines are produced continuously and reflect tumor activity rather than episodic surges. The other tests listed assess unrelated processes (cortisol production, vitamin B12 absorption, and kidney filtration) and do not measure catecholamine degradation products.