Heartworm Testing in Dogs When Why and How

Have you ever heard of heartworm disease in dogs?
It’s one of the most dangerous parasitic infections that can threaten your dog’s life if not detected early.At Daleely Medical, we provide you with everything you need to know about the Heartworm Test—why it matters, when it should be done, and how to protect your dog with effective prevention.

What Are Heartworms in Dogs?

Heartworms (Dirofilaria immitis) are dangerous blood-borne parasites transmitted to dogs through the bite of an infected mosquito. Once inside the bloodstream, the larvae grow into long worms—up to 12 inches (30 cm)—that live in the heart, lungs, and nearby blood vessels.

If left untreated, heartworms can cause:

Weakening of the heart muscle
Difficulty breathing
Chronic coughing
Heart failure
And in severe cases, sudden death

What Is the Heartworm Test?

The Heartworm Test is a simple blood test used to detect antigens released by adult female heartworms circulating in the dog’s bloodstream.

There are two main types of heartworm tests:

1. Antigen Snap Test

Provides results within 10 minutes
Commonly performed at vet clinics
Quick, accurate, and easy to use

2. Microfilaria Test

Detects baby heartworms (microfilariae) in the bloodstream
Often used as a confirmatory test following a positive antigen result

When Should Dogs Be Tested for Heartworms?

✅ For Puppies:

Testing is usually not done before 6 months of age, since heartworms take time to mature and show up on tests.
If the puppy is on early prevention, testing may be postponed.

✅ For Adult Dogs:

As part of annual veterinary checkups
Before starting any heartworm preventive medications
If the dog shows suspicious symptoms
If the dog missed a preventive dose for more than 2 months

⚠️ Common Symptoms of Heartworm Disease

Symptoms may not appear in early stages, but as the disease progresses, you may notice:

Stage	Possible Symptoms
Early	Mild fatigue, slight cough after activity
Moderate	Persistent cough, lethargy, difficulty breathing
Advanced	Swollen belly, limb edema, heart failure, sudden death

The earlier the diagnosis, the better the chances of survival.

Why Is the Heartworm Test So Important?

✅ Early detection before symptoms appear
✅ Identifies infection before starting preventive treatment
✅ Helps prevent severe heart and lung complications
✅ Protects other pets in the household
✅ A vital part of your dog’s annual health check

Is the Heartworm Test Accurate?

The antigen test is about 95–99% accurate.
However, false negatives can occur in:
- Early infections
- Infections with only male worms

That’s why your vet may recommend additional tests like:

Microfilaria testing
Or retesting in a few months

What Happens After the Test?

✅ If the test is negative:

Your vet will likely start or continue monthly heartworm prevention (tablets or topical treatments).
Recheck annually to ensure ongoing protection.

❌ If the test is positive:

The vet will create a customized treatment plan, which may include:
- Chest X-rays
- Heart ultrasound (echocardiogram)
- Targeted medications to kill the worms
- Strict rest and monitoring

⚠️ Important: Never start regular preventive medications if your dog is already infected, as killing the worms too quickly may cause dangerous blood clots.

How to Prevent Heartworm Disease

Prevention is the best defense—and it’s much easier and cheaper than treatment.

1. Monthly Preventive Treatments

Use prescribed heartworm preventives such as:

Ivermectin
Milbemycin
Selamectin

These are available as tablets or topical applications. Use them year-round, or at least during mosquito season.

2. Mosquito Control

Use safe repellents for dogs
Install screens on windows
Avoid walking your dog in areas with standing water

3. Annual Testing

Even with preventive care, no method is 100% foolproof, so annual screening is essential.

❓ Frequently Asked Questions

Can my dog get heartworms even with prevention?

Yes, although rare. It may happen if doses are missed or if the worms develop resistance. That’s why annual testing is crucial.

Are indoor dogs safe from heartworms?

Not entirely—mosquitoes can enter homes. Even indoor dogs are at risk.

Can heartworms infect humans?

Very rarely, and not in the same way as dogs. But an infected dog can still pose a risk to other pets.

✅ Final Thoughts

Heartworm testing is not just a routine check—it's a lifesaving measure.
With early detection and proper prevention, you can save your dog from severe illness or even death.