Which urinary metabolite is the end product of metabolism for both epinephrine and norepinephrine?

• A. Metanephrine
• B. Normetanephrine
• C. VMA
• D. HVA

Answer: (C)

Catecholamine breakdown converges on a common final metabolite in urine. Epinephrine and norepinephrine are first converted by COMT to metanephrine and normetanephrine, respectively. These intermediates are then further degraded by MAO to vanillylmandelic acid, which is excreted in urine. Because both pathways end at the same product, vanillylmandelic acid, it serves as the final urinary metabolite for both hormones. Metanephrine and normetanephrine are specific intermediates for each catecholamine, and HVA comes from dopamine metabolism, not directly from epinephrine or norepinephrine. Therefore, vanillylmandelic acid is the end product for both.