Diagnostic criteria for an enzyme-linked immunosorbent assay for occult heartworm disease: standardization of the test system in naturally exposed dogs.

The development of criteria for interpreting and reporting the results of an occult heartworm enzyme-linked immunosorbent assay to practitioners is described. The antigen is a saline extract of adult female Dirofilaria immitis. The cutoff absorbance A400 nm values were estimated, using 106 dogs free of infection. Any A400 nm value less than 0.526 is considered negative and values greater than or equal to 0.784 are positive. Intermediate A400 nm values are interpreted as suspect. Absorbance values for serum samples from 13 client-owned amicrofilaremic dogs revealed a bimodal distribution consistent with presumptive diagnosis based on clinical signs, which indicates that the test may be used to support a diagnosis of occult heartworm disease. The present serotest, however, is unable to distinguish microfilaremic dogs from noninfected dogs. Serum from dogs infected with other common helminths failed to crossreact with the D immitis antigen, with the exception of Dipetalonema reconditum.