BOC Clinical Chemistry Practice Test

VMA represents the final end product of catecholamine breakdown, especially from norepinephrine and epinephrine. After these amines are degraded by monoamine oxidase and then further processed by catechol-O-methyltransferase, they are ultimately converted to vanillylmandelic acid, which is excreted in urine. Dopamine is mainly metabolized to DOPAC and homovanillic acid, serotinin is an indoleamine not a catecholamine, and dihydroxyphenylalanine is a precursor to dopamine, not a metabolite. So the major metabolite reflecting catecholamine catabolism is vanillylmandelic acid.