What Is a Heartworm Test for Dogs? Everything You Need To Know

Heartworms are dangerous parasites that are transmitted to dogs by mosquitoes.

Mature heartworms live in a dog’s heart and surrounding blood vessels and cause damage to the heart and lungs. If left untreated, heartworm infections can be fatal.

Although the average infected dog has 15 adult heartworms, one dog can harbor more than 200 worms. Heartworms can grow up to a foot long.

Fortunately, these parasites are easily detected with a heartworm test for dogs. Infection can be easily prevented.

What Is a Heartworm Test for Dogs?

A heartworm test for dogs is a simple blood test performed in a veterinary clinic to determine whether a dog has heartworms.

The test requires a few drops of blood and takes only eight minutes to run. The most common test used in-office is a SNAP test that detects proteins from adult heartworms (antigens) in a dog’s blood.

Heartworms can also be diagnosed by looking for baby heartworms (microfilariae) in a drop of blood under a microscope.

Adult heartworms can also be identified while performing a heart ultrasound (echocardiogram).

However, the heartworm antigen test is typically used for detecting heartworm infections.

Heartworm tests for dogs are required annually to purchase heartworm prevention medications, which require a veterinary prescription. Because of this, heartworm tests are commonly performed during a dog’s annual wellness exam.

How Does a Heartworm Test for Dogs Work?

The heartworm test for dogs specifically detects a protein (antigen) produced by adult female heartworms.

A false negative result may occur if only male heartworms are present (which is rare in dogs), if there are only a few female worms, or if the heartworms are immature (under 6 to 7 months old).

False positives are rare but can occur if other parasites are present, such as the esophageal worm Spirocerca lupi.

Why Would a Dog Need a Heartworm Test?

A dog needs to have a negative heartworm test for a veterinarian to prescribe heartworm prevention. This is because not all preventives are appropriate for heartworm-positive dogs.

If the dog is heartworm-positive, the veterinarian will choose a preventive that has been proven safe for heartworm-positive dogs.

It’s also common for stray dogs entering animal shelters to receive a heartworm test as part of their intake care.

A heartworm test may also be recommended for a dog who has signs of heartworm disease, such as tiring easily, coughing, or weight loss.

Why Are Heartworm Tests for Dogs Important?

Heartworm tests for dogs are important because heartworm disease can be deadly. As heartworm disease advances, it causes respiratory illness and heart failure that result in suffering. Pet parents can protect their dogs with heartworm prevention.

A negative test is also necessary to purchase heartworm prevention.

A heartworm test also provides a way to ensure your pet’s heartworm prevention is effective. Treating a dog for heartworm disease can cost more than $1,000, so testing and prevention are more cost-effective than treatment.

Cost of a Heartworm Test for Dogs

Heartworm testing in dogs typically costs $35 to $75, depending on your location and the type of practice you visit.

Preparation for a Heartworm Test for Dogs

Preparation is usually not needed on the part of the pet parent prior to the heartworm test.

If your dog becomes anxious during vet visits, you may consider asking for anti-anxiety medication, such as trazodone, to help facilitate a better veterinary experience.

In most cases, blood is drawn from a vein in the front leg. A veterinary team member will usually spray alcohol on the area before drawing blood.

Occasionally, a small area of fur may be shaved to help the person drawing blood locate the vein.

How Long Do Results for Heartworm Tests Take?

The in-office heartworm test for dogs takes eight minutes to run, so pet parents can usually expect results within 10 to 15 minutes if the clinic isn’t too busy.

What To Do If Your Dog Is Diagnosed with Heartworm

It can be stressful to learn that your dog has heartworms, but the good news is that treatments are available.

Expect your veterinarian to discuss a treatment plan that includes giving antibiotics for one month, followed by a series of injections during months two and three.

They will also discuss exercise restrictions and safety concerns with you. They are likely to recommend diagnostic testing to ensure your pet is healthy enough for heartworm treatment.