Heartworm Antigen Test
An in-clinic ELISA or lateral-flow immunoassay detecting uterine glycoprotein antigens secreted by mature adult female Dirofilaria immitis heartworms.
💬 In Plain English
The heartworm antigen test is the annual screening blood test recommended for all dogs (often combined with tick screenings on a SNAP 4Dx test). Using just a few drops of blood, this test specifically detects a glycoprotein shed from the reproductive tract of adult female heartworms living inside the pet’s pulmonary artery and right heart chambers. Because the test detects mature female worms, it takes roughly 6 months after an infective mosquito bite for circulating antigens to appear. A positive antigen test must always be confirmed with a second independent test before starting adulticide injections.
🔬 Clinical & Technical Depth
For Vets & TechniciansFormal Clinical Definition
Enzyme-linked immunosorbent assay (ELISA) or immunochromatographic assay directed against somatic antigens of the reproductive tract of adult female Dirofilaria immitis, providing >98% sensitivity when at least 2–3 mature females are present.
Why Veterinarians Use It
Veterinarians perform annual heartworm tests to verify prevention efficacy and screen asymptomatic dogs before refilling prescription heartworm preventatives.
Clinical Context Encountered
Performed routinely at annual wellness examinations or when investigating canine coughing and heart failure.
Clinical Reference Guide (Diagnostic Test)
Normal vs. Abnormal Results
Normal: negative (single procedural control dot). Abnormal: distinct positive antigen dot or line (indicates presence of mature adult female heartworms).
Next Steps If Abnormal
Confirm with second independent test; perform modified Knott’s test for microfilariae; stage with thoracic radiographs and start American Heartworm Society 3-dose melarsomine protocol with doxycycline.
- •Never restart monthly heartworm preventatives on a dog without testing first: if a heavy microfilaria worm burden is present, preventatives can cause rapid microfilarial death and fatal anaphylactic shock.
❓ Questions to Ask Your Veterinarian
Take these actionable questions with you to your next clinic visit or appointment:
- 1If positive, has a confirmatory test (from a different lab or different test platform) and a microfilaria check been performed?
- 2Has my dog been screened for heartworm microfilariae using a Knott’s test or blood smear?
- 3Are chest X-rays needed to evaluate pulmonary artery enlargement and lung inflammation?
Academic & Clinical References
- Current Canine Guidelines for the Prevention, Diagnosis, and Management of Heartworm (Dirofilaria immitis) Infection in DogsOrganization: American Heartworm Society (AHS) • Accessed: 2026-01-10https://www.heartwormsociety.org