Performance of SNAP® 4Dx® Plus and AccuPlexTM4 in Dogs with different Heart- worm Burdens

SNAP® 4Dx® Plus (IDEXX Laboratories, Westbrook, ME) is a commercially available in-office test kit for the simultaneous detection of Dirofilaria immitis antigen and antibodies to Anaplasma phagocytophilum, A. platys, Borrelia burgdorferi, Ehrlichia canis, and E. ewingii in blood, plasma, or serum of dogs. AccuPlexTM4 test (ANTECH Diagnostics®, Irvine, CA) is a recently launched reference laboratory test that detects heartworm antigen and antibodies to Lyme disease, anaplasmosis, and ehrlichiosis in dogs. In this report, we compared the performance of SNAP® 4Dx® Plus and AccuPlexTM4 for detection of heartworm antigen in sera from dogs having necropsy-confirmed infections with a broad range of worm burdens. A total of 72 necropsy confirmed samples with a wide range of worm burden and 21 negative samples confirmed negative by PetChek® Heartworm PF Antigen Test (IDEXX Laboratories, Westbrook, ME) were used in this evaluation. Of the 72 necropsy-confirmed samples, SNAP® 4Dx® Plus test detected 65 samples compared to 54 samples detected by AccuPlexTM4 assay. The AccuPlexTM4 assay reported a positive result for one antigen negative sample. For the low-worm burden populations, SNAP® 4Dx® Plus detected 82% of dogs with one worm and 100% of dogs with two worms, while AccuPlexTM4 only detected 53% of dogs with one worm and 86% of dogs with two worms, respectively. In this study, where a direct comparison of the test methodologies was performed using the same sample set, the results indicate that SNAP® 4Dx® Plus is more sensitive than AccuPlexTM4 in detecting heartworm antigen in dogs with low worm burdens.