Why does my pet need a heartworm test if they are on heartworm prevention drugs?

Why test for heartworms if my dog has been on heartworm prevention medication?

Hi. This question is from Susan from New Orleans. The question is: “If I’ve been giving heartworm prevention for the past year to my dog, why do I have to do a heartworm test before I can buy more prevention?”

Dogs must be heartworm-negative before taking heartworm prevention medication

The answer from the FDA, who licenses the drugs, is that a veterinarian must confirm that the dog is heartworm-negative before the dog can have heartworm prevention. And while I believe that my client had been giving the heartworm prevention, I can’t, unless I was giving the heartworm prevention, certify that the dog is likely negative unless I do the heartworm test. So the FDA is saying to the doctor, “You must only prescribe this medication to a heartworm-negative dog.” The only way I can ensure it is a heartworm-negative dog is by doing the heartworm test.
Thank you very much.