What is a heartworm antigen test?
A blood test that detects proteins produced by adult heartworms in an infected dog's bloodstream, used to diagnose heartworm disease.
A heartworm antigen test is a blood screening that identifies proteins (antigens) released by adult female heartworms into the bloodstream. The test works by drawing a small blood sample and analyzing it for the presence of these specific proteins, which only appear once heartworms have matured to adulthood, typically 6-7 months after initial infection. Results are usually available the same day or within 24 hours.
The test is considered highly accurate for detecting infections once adult heartworms are established. However, it will not catch very early infections before worms have matured, and dogs with only male worms may test negative. For this reason, veterinarians sometimes recommend a second testing method (like an antibody test or ultrasound) if heartworm disease is suspected but the antigen test comes back negative.
In Colorado, where heartworm transmission occurs year-round due to indoor pets and migratory wildlife, annual antigen testing is standard practice for dogs on prevention medication. Testing before starting prevention confirms the dog is not already infected, and annual follow-up testing ensures the preventive is working. Dogs not on prevention should be tested at least once yearly, particularly if they spend time outdoors or travel to warmer regions. Your veterinarian can recommend the best testing schedule based on your dog's lifestyle and risk factors.