Q: Do I have to test my dog for heartworm disease?

Original Question: "Is the heartworm test for a 3-year-old Pomerania needed? How often? Thanks." -  Tania

Vet Certified Answer | Answered: April 1, 2018

Hi Tania,

Thanks for your question.

This is a complicated question that would likely result in different answers depending on the veterinarian answering. I'm going to give you some concepts to consider to empower you to make the decision yourself.

The chance of your dog contracting heartworm will vastly differ based on where you live. You should ask your veterinarian about the potential risk in your area. Here, in Toronto Canada, the risk would be about 1 in 1000 to 1 in 10,000. Although the risk may be low, the impact if it did occur is very serious and could impact your pet's health permanently. Many people use preventives because they are very effective and completely eliminate the risk.

- We perform a heartworm test to confirm that your pet does not have heartworm before the preventive medication is given. There is a risk of an allergic reaction or even the preventive medication killing the heartworms within the vessels and causing a blockage or embolism. The risk of this depends on the type of medication being given and you discuss this with your veterinarian. By testing your dog first, you eliminate the chance of a reaction because you'll know if your dog has heartworms before the medication is given. A blood test is quick and noninvasive so people tend to do it to eliminate the risk. The downside would be the cost which you have to consider yourself.

- If you gave your pet the preventive medication throughout the previous year's heartworm season, many people believe the heartworm test is unnecessary. It's true that your pet's chance of having heartworm disease is then extremely unlikely, but there is still a possibility that heartworm was contracted for reasons such as skipping a dose, improper application or delivery of the medication, inactivated medication from improper storage, handling or manufacturing. Keep in mind that your veterinarian may require you to sign a waiver if you decline the heartworm test because they can't be certain if the preventive was given in the previous year and they don't want to give a potentially harmful medication to your pet.

- I've found that my clients have very different feelings about the risks, benefits and costs of testing and preventing heartworm. It's important to educate yourself and hopefully your veterinarian gives you an unbiased evaluation of your unique situation so you can make the decision yourself. Many people feel that their veterinarians simply have a blanket recommendation for testing and preventing heartworm disease and that they don't evaluate everyone's needs individually. Keep in mind that they also want to control the disease across their community rather than just one pet.

I encourage you to watch our videos on heartworm for more information about the risk, testing and prevention of the disease.

I hope this helps!

Dr. Clayton Greenway

Disclaimer: and its team of veterinarians does not endorse any products or services mentioned. Advice presented by our veterinarians is not meant to replace a regular physical exam and consultation with your primary veterinarian. We always encourage you to seek medical advice from your regular veterinarian.

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