Detection of circulating Dirofilaria immitis antigens in random source laboratory dogs: evaluation of two commercial serodiagnostic tests.

Two commercially available serodiagnostic tests for Dirofilaria immitis antigens were evaluated for sensitivity, specificity, predictive values, and reliability using serum from 110 random source dogs. Both tests were performed in two separate laboratories on serum samples randomized in five blocks of 22 samples each. Dogs were examined for microfilariae using the modified Knott's technique, and for adult parasites by necropsy. Forty-eight of the 110 dogs (43.6%) had either adult or juvenile parasites within the cardiopulmonary vasculature or microfilariae in the peripheral blood. Of those 48, 26 (54.2%) were amicrofilaremic and had cardiopulmonary parasite populations ranging from one to greater than 50. In both laboratories, both commercial tests failed to detect infection in eight of the 26 amicrofilaremic dogs. Three amicrofilaremic dogs were positive by both tests in both laboratories. Four dogs (3.6%) had microfilariae without adults. Two of those four dogs were negative by both commercial tests in both laboratories. One commercial test had 38 false negatives in one laboratory, 13 of which were also negative in the second laboratory. The other test had 21 false negatives in one laboratory and 20 in the other laboratory. Fourteen of these samples were falsely negative in both laboratories. False positives were low in both laboratories for both tests.