Improved colorimetry of urinary 3-methoxy-4-hydroxyphenylacetic acid (homovanillic acid).

Homovanillic acid is an important metabolite of dopamine, and a high proportion of patients with neuroblastoma excrete increased amounts of it in their urine. When this diagnosis is suspected, both homovanillic acid and vanilmandelic acid should be measured, because such a combined measurement reportedly leads to detection of 95% of cases. Although rapid and reliable chemical methods are available for vanilmandelic acid, the same is not true for homovanillic acid. We report here a colorimetric method for homovanillic acid that reasonably fills this void and that can be used in most clinical laboratories. In addition, we present normal values determined for children of various age groups.