Why Does My Pet Need An Exam Or Bloodwork To Receive A Heartworm Preventative?

Each year, heartworm affects about 250,000 pets nationwide. A dangerous parasite, a single heartworm can grow up to 12 inches in length and resides within the chambers and vessels of your pet’s heart. Symptoms of heartworm include cough, lethargy, fatigue, loss of appetite, and weight loss. If left untreated, heartworm can seriously impede your dog’s cardiac function and in severe cases may be fatal.

The good news is that heartworm is 100% preventable! So why does getting a heartworm preventive require pre-administration testing?

How Would My Pet Get Heartworms?

Heartworm is a vector-borne parasite, which means that it cannot be transmitted from host to host without an agent, such as a mosquito, tick, flea, or other parasite. For example, a mosquito bites a dog that is already infected with heartworm. Along with a small amount of the host’s blood, the mosquito takes the tiny heartworm larvae called microfilariae. When the mosquito then bites an uninfected animal, it introduces the heartworm larvae, passing on the infection. Heartworms can only be transmitted from animal to animal by mosquitoes. For animals who are not on preventatives, when an infected mosquito bites your pet, young heartworms enter into your pet’s system.

What Pets Should Be Tested for Heartworms?

Because heartworms are spread by mosquitoes, any pet exposed to mosquitoes should be tested, even those that only go outdoors occasionally. Also, remember that mosquitoes can also get into homes, putting indoor-only pets at risk as well.

What Should I Do If My Pet Has heartworms?

Treatment of an already infected animal depends on several factors, including the type of pet you have and the overall health of your animal.


There is currently no effective and safe medical treatment for heartworm infection or heartworm disease in cats. If your cat is diagnosed with heartworms, your veterinarian may recommend medications to reduce the inflammatory response and the resulting heartworm disease, or may suggest surgery to remove the heartworms.


Treating an infected dog for heartworms has its risks. However, serious complications are much less likely in dogs that are in otherwise good health and when you carefully follow recovery instructions. Once heartworm disease is diagnosed, your pet will go through an array of treatments over several months. The time from initial treatment to complete recovery can be as much as one year.

The American Heartworm Society recommends testing pets every 12 months for heartworm and giving your pet a heartworm preventive 12 months a year. Have questions or need to get your pet tested? Give us a call and make an appointment. Our skilled and friendly staff are here to help.

Why Pre-Administration Testing Matters

Heartworm preventatives are extremely effective; however there are some important cautions that make pre-administration testing necessary.

So even if your pet is already receiving heartworm protection, there is still a small chance your pet is infected. Giving certain types of heartworm preventatives to an already infected animal may be dangerous.

No medication is 100% effective in all animals

Missing or even delaying a scheduled dose of heartworm preventative could expose your pet to the risk for infection. And in its early stages, heartworm produces few or no symptoms, so you may not know your animal is affected.

Maybe you missed a dose

At Richmond Road, we employ a test that not only screens for heartworm, but also evaluates tick exposure by searching for antibodies to other parasite-borne illnesses, including Lyme disease, Ehrlichiosis , and anaplasmosis. Also, when adult worms die, they collapse and are pushed deeper into the smaller branches of the vessels that supply blood to the lungs, increasing the risk for vessel obstruction, which can result in severe complications and possibly death. By scheduling an exam and bloodwork before a heartworm preventative is prescribed, you can vastly reduce these risks.

Not all heartworm tests are the same