Assessing the performance of trūRapid™ FOUR heartworm antigen test for early detection in experimentally infected dogs in comparison to other point-of-care tests.

BACKGROUND: The American Heartworm Society (AHS) recommends diagnosing canine heartworm (HW) infection using both antigen and microfilaria detection tests. Antigen-antibody immune complexes may block antigen detection. Therefore, the AHS recommends immune complex dissociation (ICD) via heat treatment for discordant cases. The trūRapid™ FOUR antigen test kit (Antech Diagnostics) is a novel commercially available point-of-care (POC) device. This study evaluated the performance of trūRapid™ FOUR compared to other commercially available POC tests, namely SNAP® 4Dx® Plus (IDEXX), VETSCAN® Flex4 (Zoetis), and a plate-based assay, DiroCHEK® (Zoetis), for early detection of HW infection in experimentally infected dogs. METHODS: Archival frozen serum samples from six purpose-bred beagles experimentally infected with Dirofilaria immitis were collected weekly for 5.5 months, from week 1 to week 22 post-infection. Sera were tested for the detection of HW antigen, pre- and post-ICD, via heat treatment (103 °C for 10 min in a heat block) using each of the commercial antigen tests. DiroCHEK® results were interpreted using optical density readings. RESULTS: HW antigen was not detected in samples collected from week 1 through week 19. In week 20, the trūRapid™ FOUR, SNAP® 4Dx® Plus, and VETSCAN® Flex4 detected HW antigen in one out of six samples (16.7%) post-ICD, while DiroCHEK® detected two (33.3%) post-ICD. In week 21, the trūRapid™ FOUR, SNAP® 4Dx® Plus, and DiroCHEK® detected HW antigen in four out of the five (80%) post-ICD samples, whereas the VETSCAN® Flex4 detected three out of the four (75%) post-ICD samples. In week 22, HW antigen was detected in one of six (16.7%) pre-ICD by all tests; trūRapid™ FOUR, SNAP® 4Dx® Plus, and DiroCHEK® detected HW antigen on all six (100%) samples post-ICD, while VETSCAN® Flex4 detected four of six samples (66.7%). CONCLUSIONS: Our findings indicate that trūRapid™ FOUR and other commercially available antigen detection tests can detect HW antigen as early as 5 months post-infection when serum is subjected to heat treatment. The performance of trūRapid™ FOUR is comparable to other widely used commercial antigen kits. Its ease of use and ability to detect HW infection earlier in the course of antigenemia makes it an excellent POC diagnostic tool, allowing for prompt clinical intervention, and increasing patient quality of life.