vanillylmandelic acid (VMA) /vənil′ilməndel″ik/ , a urinary metabolite of epinephrine and norepinephrine. It may be measured in the urine to determine the levels of these catecholamines. A greater-than-normal amount of VMA is characteristic of a pheochromocytoma or neuroblastoma. Increased concentrations of this acid may raise the blood pressure and indicate the presence of tumors of the adrenal glands or nervous system, muscular dystrophy, and myasthenia gravis; they may be caused by stress, exercise, or certain drugs or foods. Normal amounts in the urine of adults after 24-hour collection are 1.5 to 7.5 mg; in the urine of infants, it is 83 mg/kg of body weight. Also called 3-methoxy-4-hydroxymandelic acid.
