How Often Does My Pet Need a Heartworm Test?

It is important for pets to be tested annually for heartworms.

One of the most common questions asked of veterinarians is how often pets need to have a heartworm test.  Both the American Veterinary Heartworm Society and most veterinarians do recommend yearly heartworm testing.   Even though many animal guardians keep their pets on year-round heartworm medication, it is still important to test pets yearly for several reasons.

One of the most important reasons for an annual heartworm test is that, even though most products are highly effective in preventing heartworm infection, there is still no product that is 100% effective.  I have seen many cases in my 20-year veterinary career of pets on year-round heartworm preventative medication that have tested positive for heartworms.  There has also been increasing recent concern about developing heartworm resistance to some of the older products, and until this issue is sorted out, it is still best to have all pets tested every year.   Also in the possibility that a pet is heartworm positive, there can be very occasional severe and even rare fatal reactions should a pet that is positive for heartworms continue to receive monthly preventative.

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  1. Dr. Michael Dym, VMD veterinarianAugust 6, 2014 at 7:49 pm

    No law Sharon, but most vets are following the recommendations of the American Veterinary Heartworm society on annual testing. Also some of the preventatives are no longer 100 percent effective anymore, due to some emerging heartworm resistance being seen; thus the annual testing.

  2. Yeah, it is still a money maker for the vet. Just like all the other unnecessary tests.

  3. My 11-yr. old Cocker Spaniel had surgery on his gums 2 months ago to remove a growth. The biopsy first said the growth was a fibromatous & ossifying epulis. Then after the removal, the biopsy said it could be a fibrosarcoma or a acanthomatous epulis – the pathologists couldn’t agree. I was told to be vigilant for the next 5 months to make sure the growth doesn’t reappear. I feel wary about giving my dog Revolution heartworm preventative since no one is really sure what this growth was. Also, the vet says there seems to be a slight enlargement in a lymph node, but this could be from the sebaceous cyst on his ear or gingivitis. Do you think it would be safe to start Revolution again? My vet thinks it’s OK, even though my dog has not been given Revolution for 2 months. Just wanted your opinion. Thanks!

  4. Dr. Michael Dym, VMD veterinarianSeptember 12, 2014 at 4:22 pm

    HI Mindy. While topical revolution is an excellent product for flea and heartworm control, any topical and/or oral pesticide may have the potential to aggravate his body’s detoxifying mechanisms, when used chronically over time, which can be important with case that we are not sure about cancer in the mouth. I think revolution is one of the safer of the pesticides we use, however if you are very concerned then using natural flea/heartworm control may be an off label option for you. See the website for some suggestions

  5. I am on SS and thus get a check once a month that allows me to just make it thru the month. My problem is my check isn’t always on the same date each month. I’ve had my dog on monthly heartworm/flea meds. My vet insists that if I am even just a few days past the due date on the dogs meds that he has to have the heartworm test done all over again before I can get the next dose. Is this accurate? I can’t afford to buy more than one month at a time and the testing is going to be getting pretty expensive at this rate. I have to do what’s best for my dog, though. Your input would be much appreciated. Do the monthly doses ‘have’ to be fairly exact as to date administered?

  6. Dr. Michael Dym, VMD veterinarianOctober 23, 2014 at 10:31 pm

    Hi Julee. Actually there is several week safety factor for many heartworm preventatives. For example, ivermectin, the main ingredient in heartguard or iverhart, protection lasts up to at least 6 weeks and possibly up to 3 months. So no worry about being EXACTLY on time each month

  7. Sharon, if you live near Waco, the Animal Birth Control Clinic does heartworm tests for $10.

  8. Hi, my 5 year old labradour, was tested for heartworm last month came back neg. They want to test him again in april 2016 because apparently he is 105 pounds and they said i did not give the right dosage for his weight. I gave him heartgard for up to 100 pounds but i did not give him heartgard blue for 25 pounds.Now would that have a made a difference. Is there a chance that he could develop heartworms in the next 6 months. I give him the exact dosage now. The brown and the blue.And would the heartgard kill the larve.

  9. I have a dog that needs heart and eye medications, and when I was shopping around 800PetMeds was far more expensive than some other online companies. I eventually went with Drs. Foster & Smith.

  10. I had my dog tested today for heartworm and it’s only cost $15.00. 2/2/17

  11. Thank you Penny. That is a VERY reasonable price for this important and recommend annual heartworm blood test

  12. Just responding to some comments about tests being “money makers” for vets. Everything a veterinarian does needs to produce revenue like any other business. Otherwise they wouldn’t be in business.

  13. Hi Anne. Thank you. YES, veterinary medical practice is indeed a small business, and there is profit involved in them staying open as well, in addition to their hearts of providing hopefully the best quality medical care for their patients.

  14. Forest South Animal Hospital will not let me get your heart worm meds even though my dog was tested already this year.

  15. HI CJ. By Law and veterinary state practice standard acts(you can check out or call your local state board), vets must provide written prescriptions to pets who are current on heartworm testing to clients to fill where they may like

  16. Once I get my dog tested and started on the yearly injections, do you think the yearly tests are then necessary?

  17. One of the main problems you’ll face is of course deadline stress.

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