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Medical Definition of Homovanillic acid
1. A test that measures the level of catecholamines or their metabolites in the urine. A 24 hour urine sample is necessary for this assay. Elevations may be seen in pheochromocytoma or neuroblastoma. Normal urine levels of adrenaline should be: 0.5 to 20 mcg/ml and normal urine levels of noradrenaline should be 15 to 80 mcg/ml. (27 Sep 1997)