This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pathology
The most reliable test in the diagnosis of pheochromocytoma is 
Select and explain. 
A. 24 hour urinary metanephrine, B. Urinary catecholamines, C. Urinary catecholamines, D. Basal plasma catecholamines
A: 24 hour urinary metanephrine
Answer: A: 24 hour urinary metanephrine 
Explanation: 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