In patients with renal impairment, which screening test is preferable for pheochromocytoma and why?

• A. Serum cortisol
• B. Plasma-free metanephrines or 24-hour urinary metanephrines; plasma tests are less impacted by renal dysfunction
• C. Plasma catecholamines
• D. Dexamethasone suppression test

Answer: (B)

Metanephrine testing is used because pheochromocytomas continuously release these metabolites, making them more reliable markers than the catecholamines themselves. In the setting of kidney disease, measuring metanephrines in plasma is preferred because plasma-free metanephrines remain more robust and are less affected by reduced renal function than urinary measurements. If plasma testing isn’t available, a 24-hour urinary metanephrine test can be used, but plasma testing is typically more reliable when renal impairment is present. The other tests aren’t appropriate screens for pheochromocytoma: serum cortisol and the dexamethasone suppression test assess other endocrine conditions, and plasma catecholamines can miss pheochromocytomas due to episodic release and greater sensitivity to stress and kidney function.