Sensitivity and specificity of the indirect-fluorescent antibody test and two enzyme-linked immunosorbent assays in canine dirofilariasis.

Ninety dogs naturally infected with Dirofilaria immitis and 103 noninfected dogs, as determined by necropsy, were used to compare the sensitivity and specificity of the cuticular and somatic reactions of the indirect fluorescent antibody test (IFA-C and IFA-S, respectively) and 2 enzyme-linked immunosorbent assays (ELISA). In microfilaremic and amicrofilaremic heartworm-infected dogs, negative results were common for all serotests. In dogs without adult heartworms at necropsy, 32% to 49% were positive, using 1 ELISA, 27% to 29% were positive with the other ELISA, 15% to 36% were positive with the IFA-S, and 0% to 1% were positive using the IFA-C, depending on the classification of borderline reactions. The prevalence of false positive serotests was probably not due to the detection of precardial stages of D immitis in dogs obtained from areas of low endemicity. Until the causes of the false-positive tests are resolved, the use of currently available serotests for routine diagnostic screening or as criteria for instituting treatment is not recommended.