Is annual Dirofilaria immitis antigen testing at preventive renewal proportionate to the residual infection risk in documented-compliant dogs?

Annual heartworm testing in documented-compliant dogs may not be proportionate to infection risk across all geographic regions.

This study critically evaluates the American Heartworm Society (AHS) guideline recommending annual Dirofilaria immitis antigen testing at every preventive renewal, regardless of a dog's compliance history or geographic heartworm prevalence. The author applies Number Needed to Screen (NNS), a well-established framework in human preventive medicine, as a novel veterinary screening tool to assess whether blanket annual testing is proportionate to actual infection risk in documented-compliant dogs. Using county-level Companion Animal Parasite Council (CAPC) prevalence data and the compliance-gap distribution as a proxy for infection risk, the study derives geographically stratified NNS estimates that vary approximately 25-fold across US states. This substantial geographic variation suggests that a one-size-fits-all testing mandate may not be clinically proportionate in low-prevalence regions with documented-compliant patients. The author argues that current AHS guidelines, which classify prescribing macrocyclic lactone preventives without antigen testing as 'NOT RECOMMENDED,' do not account for meaningful differences in regional risk or individual compliance history. A risk-stratified screening approach—calibrated to local prevalence and patient compliance documentation—is proposed as a potentially more efficient and evidence-based alternative. The study calls for prospective evaluation of this framework. While this is a modeling-based analysis rather than a clinical trial, it introduces a quantitative, patient-centered lens to a guideline that has historically been applied uniformly, prompting important discussion about resource allocation and individualized preventive care strategies.

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