An important part of a complete heartworm prevention program is testing. Testing ensures that your pet is free of adult heartworms, and ready to start or continue on heartworm preventive medication. The American Heartworm Society (AHS) estimates that only 50% of dogs in areas where heartworm occurs are actually on heartworm preventives. Of those prescribed heartworm prevention products, only about 75% receive all of the doses. Since heartworm continues to be a fatal disease and pet owners’ compliance with heartworm prevention is less than optimal, the AHS recommends the following guidelines for testing and giving preventives.


  1. All dogs should be tested annually for heartworm infection. Since not all pets receive the proper dose of preventives, the AHS recommends a more conservative testing routine than in the past. Annual testing ensures that an infection is caught in plenty of time to effectively manage it. The AHS also recommends that cats be tested prior to being started on a preventive.
  2. Dogs should be tested for heartworm if they are going to be switched from one preventive to another. If a pet owner switches between preventives, there are specific time periods in which their pet should be retested in order to ensure the pet is protected. It is, therefore, necessary to test more often.
  3. Puppies under seven months of age can be started on heartworm preventives without first being tested. This is because it can take up to six and one half months after being bitten by infected mosquitoes before the dog will test positive. The puppy should be tested four to seven months after starting heartworm preventive to detect any infection acquired during the first few months of life. Consult with your veterinarian to determine the right testing schedule for your pet.

Types of Tests
There are different types of heartworm tests, which require a blood sample from your pet.

Antigen Tests
These tests detect specific antigens from adult female heartworms, and are used with much success to detect canine heartworm infection. Currently, tests are available as in-clinic tests, as well as at many veterinary reference laboratories. Most commercial tests will accurately detect infections with one or more mature female heartworms that are at least seven or eight months old, but they generally do not detect infections of less than five months duration.

Antibody Tests
In the late 1970’s and early 1980’s, several canine heartworm antibody tests were developed and introduced, but such tests for dogs have been largely replaced by the more useful antigen tests. The antibody test is the most common test used in cats, however.

Healthy and Heartworm-free: Everyone’s Goal

There is no maternal transfer of protection against heartworms. If puppies or kittens are exposed to mosquitoes carrying infective larvae, they can be infected. In areas with year-round potential for infection, puppies and kittens should be started on a heartworm preventive by no later than eight weeks of age.

In the battle against heartworm disease, it is better to be “safe than sorry.” Heartworm testing is an important part of a heartworm prevention program. Your veterinarian will help you determine the right testing schedule for your pet. Negative results help determine your pet’s overall health and rule out the presence of heartworm disease.