The most reliable test in the diagnosis of pheochromocytoma is

Pheochromocytomas are neoplasms of chromaffin cells,which synthesize and release catecholamines. The lab diagnosis of this condition is based on demonstration of increased urinary excretion of free catecholamines and their metabolites; vanilylmandelic acid and metanephrines. (ref:ROBBINS Text book of pathology