Why do dogs need blood tests before starting Heartworm disease prevention medication?
Before starting Heartworm prevention, veterinarians test to make sure the pet doesn’t already have a Heartworm infection. Giving Heartworm disease prevention medications to pets that already have infections can cause severe illness, or death. Pets less than 7 months old can begin Heartworm prevention without testing but the vet may recommend testing 4-7 months after starting the medication. This is because it takes 6-7 months after being infected for microfilariae to mature to the point they produce a positive test.