What is the best single screening test for pheochromocytoma using 24-hour urine?

The best single screening test for pheochromocytoma using a 24-hour urine collection is the measurement of metanephrines. Pheochromocytomas are tumors of the adrenal glands that produce excess catecholamines, leading to increased levels of both metanephrines and catecholamines in the urine. Metanephrines, which include normetanephrine and metanephrine, are more stable metabolites of catecholamines and are found in elevated levels in patients with pheochromocytoma, even in cases where catecholamine levels may fluctuate.

Due to this increased stability and the fact that metanephrines are produced continuously by the tumor, testing for urine metanephrines provides a highly sensitive screening method. This is particularly important since pheochromocytomas can sometimes be difficult to detect based on catecholamine levels alone, which may vary based on stress or other factors. Thus, measuring metanephrines in a 24-hour urine sample offers a reliable and effective approach to diagnosing pheochromocytoma.