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How to Read a Heartworm Test

Updated on October 8, 2011

Heartworm Test

When you take your dog to the vet for his/her yearly vaccinations and exam, it is always a good idea to have your veterinarian run a heartworm test. Even if your dog stays inside most of the time, or if you regularly administer a heartworm prevention, you still want to make sure that you have the test run.

It is always better to have the test run, as a precaution so that you can treat a case of heartworms before it gets severe.

Never think that just because you administer a preventative your dog is 100% safe from contracting heartworms. I know at least one person who's dog tested positive for heartworms, even with the monthly HeartGuard medication.

SNAP Heartworm Test

The most common form of heartworm test is going to be the SNAP heartworm test. These are cheap for your veterinarian to purchase, which means it's cheap for you. These tests are reliable, quick, and easy to read, so instead of waiting a few weeks, you only have to wait 5 to 10 minutes.

When your vet tests your dog's blood for heartworms, the vet will use enough blood to fill top circle, which is the sample well. The blood will saturate the middle test strip on the SNAP heartworm test and then slowly disappear. Where you once saw four blue dots, the dots will have disappeared. After the proper time has elapsed, about 8 minutes, there will be one dot to appear.

Depending on where the dot appears on the test, will determine whether or not your dog has heartworms.

Click thumbnail to view full-size
Heartworm negative
Heartworm negative
Heartworm negative

Reading a Heartworm Test

SNAP Heartworm Tests are pretty easy to read, and as long as you know what you're looking for, you may know your dog's results before your veterinarian comes back to tell you. I personally, used the below information to read my bull mastiff's results before her vet came back to the room.

Depending on where the blue dot reappears, you'll know whether or not your dog has heartworms or not.

  • Top dot - Positive control is present, which means your dog is negative for heartworms
  • Left dot - high antigen levels
  • Right dot - low antigen levels
  • Bottom dot - Negative control is present, which means your dog is positive for heartworms

The test will need to be repeated if:

  1. The positive control did not appear on the sample area (top dot)
  2. A circle is present on the negative control area (bottom dot)
  3. If any of the dots are equal to or darker than another dot
  4. The background color interferes with properly reading the results.

Note: It takes 6 to 7 months before any heartworm test can detect heartworms, which means that your dog may have been infected but the test will not read accurately within the first 6 months. This is why you need to test your dog for heartworms annually. It's also a good idea to ensure that your dog receives proper heartworm preventative.

Pet Alive Parasite Dr.

PetAlive is a great all natural series of holistic dog medications. Parasite Dr. is specially formulated for the expulsion of internal parasites, such as roundworms, heartworms, and tape worms. The holistic medication contains herbs that are known for their anti-parasitic, antiseptic, and bactericidal properties.

This holistic dog medicine not only gets rid of internal parasites, but it also soothes the digestive system, reduces problems related to parasites such as malnutrition and restlessness, detoxes the digestive system, improves digestive functions, reduces gas, and protects against bacterial and yeast infections.


Please be aware that the advice in this article should in no way replace that of a licensed veterinarian. If you have any questions or concerns, you should consult a veterinarian.


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