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Administration of L-dopa may falsely increase homovanillic acid (HVA) results. Patients receiving L-dopa should stop taking it for 24 hours before and during the collection.
All patients receiving L-dopa should be identified to the laboratory when vanillylmandelic acid (VMA) and HVA tests are ordered.
All patients taking Bactrim should be identified to the laboratory when VMA and HVA tests are ordered due to potential interference.
Vanillylmandelic acid (VMA) and/or homovanillic acid (HVA) concentrations are elevated in over 90% of patients with neuroblastoma; both tests should be performed. A positive test could be due to a genetic or nongenetic condition. Additional confirmatory testing is required.
A normal result does not exclude the presence of a catecholamine-secreting tumor.
Elevated HVA values are suggestive of a deficiency of dopamine beta-hydrolase, a neuroblastoma, a pheochromocytoma, or may reflect administration of L-dopa.
Decreased urinary HVA values may suggest monoamine oxidase-A deficiency.