trūRapid FOUR detected heartworm antigen in all six experimentally infected beagles by week 22 when their serum was heat-treated, according to a study examining early detection with four point-of-care assays. The authors say the test can detect antigen as early as five months after infection once antigenemia is established, meaning antigen is present in the blood. The experiment did not measure whether earlier detection changed treatment, clinical outcomes or quality of life.
What the researchers tested
The research question was whether trūRapid FOUR could identify heartworm antigen early and how its results compared with SNAP4DxPlus, VETSCANFlex4 and DiroCHEK. The researchers used archived serum from six purpose-bred beagles. Each dog had been inoculated under the skin with 50 infective L3 of Dirofilaria immitis, the heartworm species used in the experiment. Blood was collected weekly from week 0 through week 22, and the serum was stored at minus 80 degrees Celsius.
Each sample was tested once with each assay when there was enough serum. The researchers tested untreated aliquots and matching samples after immune complex dissociation, or ICD, a heat-based preparation step used before testing. For the post-ICD samples, 400 microlitres of serum was heated to 103 degrees Celsius for 10 minutes and then centrifuged at 16,000 times gravity for another 10 minutes. The methods did not report randomization or a separate uninfected control group.
Positive results appeared late, then rose sharply
No assay detected heartworm antigen in serum collected from week 0 through week 19, whether the samples were untreated or had undergone ICD. At week 20 after ICD, trūRapid FOUR, SNAP4DxPlus and VETSCANFlex4 each detected antigen in one of six dogs, or 16.7 percent. DiroCHEK detected antigen in two of six dogs, or 33.3 percent.
At week 21 after ICD, trūRapid FOUR, SNAP4DxPlus and DiroCHEK were positive in four of five available samples, or 80 percent. VETSCANFlex4 was positive in three of four samples, or 75 percent. The denominators were not the same because serum volume limited testing at that time point, with five dogs available but only four providing enough material for VETSCANFlex4.
The difference between untreated and heat-treated samples was clearest at week 22. Before ICD, every assay detected antigen in one of six samples, or 16.7 percent. After ICD, trūRapid FOUR, SNAP4DxPlus and DiroCHEK each detected antigen in all six samples, or 100 percent, while VETSCANFlex4 detected it in four of six, or 66.7 percent. These figures describe detection in this experiment; they are not estimates of how accurately the tests perform across the wider dog population.
The comparison does not establish a clear winner
For the formal comparison, the researchers used Cochran's Q test to examine differences in positivity across assays and time points. They then used paired McNemar tests with a Bonferroni correction, which adjusts for multiple comparisons. The overall assay comparison was reported as statistically significant, with a P-value below 0.001, but the corrected pairwise comparisons were not significant for untreated-versus-untreated, heat-treated-versus-heat-treated or untreated-versus-heat-treated comparisons.
Only four of the six dogs had complete data for the paired analysis. The authors say the post hoc comparisons were underpowered, meaning the dataset was too small to make those individual comparisons reliably. That matters because the striking week 22 pattern should not be read as proof that trūRapid FOUR is better than the other assays. The authors instead conclude that its performance after ICD was comparable to widely used point-of-care tests.
What remains unanswered
The evidence comes from six purpose-bred beagles infected under controlled experimental conditions and followed for 22 weeks. It does not show how the assays perform in naturally infected dogs with different worm burdens, isolates, preventive histories or microfilaremia status. The study evaluated only the Metairie isolate, and each sample was tested once, limiting what it can say about isolate-specific differences and technical repeatability.
The study also did not include a reported separate uninfected control group, and it measured antigen detection rather than patient care. No treatment, clinical outcome or quality-of-life endpoint was recorded. Further work would be needed to determine whether finding antigen at an earlier time changes clinical decisions or benefits dogs.
Funding and disclosures
The project was funded by Antech Diagnostics. The competing-interests declaration identifies listed authors as employees of Antech Diagnostics or Mars Petcare Science & Diagnostics, or of Texas A&M University. The manuscript states that data supporting its main conclusions are included in the article.
Paper data and sources
Original title: Assessing the performance of trūRapid™ FOUR heartworm antigen test for early detection in experimentally infected dogs in comparison to other point-of-care tests.
Authors: Pabasara Weerarathne, Tiana L Sanders, Alexa Starnes et al.
Journal/Repository: Parasites & vectors
Status: Peer-reviewed
First online: 2026-08-20
DOI: 10.1186/s13071-026-07450-w
Original paper · Full text