The ELISA procedure utilizes the excretory-secretory(es) antigen of T. canis larvae to minimize cross-reactivity with antigens of Ascaris spp. and of other parasites. Results must be interpreted with caution as broad variations in antibody response occur and levels may remain elevated for years after infection. Generally, antibody levels are highest in visceral larva migrans (VLM). A negative result usually rules out infection with Toxocara spp.