Keywords: heartworm tests for dogs, canine heartworm testing, when to test for heartworms, heartworm symptoms, heartworm prevention, dog health checkups
Heartworm disease is a serious and potentially fatal condition in dogs, caused by a parasitic worm called Dirofilaria immitis. These worms live in the heart, lungs, and associated blood vessels of infected pets, causing severe lung disease, heart failure, and other organ damage. Early detection through heartworm tests is critical to protect your dog’s health.
In this article, we’ll dive deep into everything you need to know about heartworm testing in dogs—why it’s important, how it’s done, when to test, and what the results mean.
What Is Heartworm Disease?
Heartworm disease is transmitted through mosquito bites. When a mosquito bites an infected animal, it picks up microscopic baby worms (microfilariae), which develop into infective larvae. When the mosquito bites another dog, it passes the larvae into the dog’s bloodstream, where they migrate to the heart and lungs.
Key Facts:
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It takes about 6 months for the larvae to mature into adult heartworms.
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An infected dog can have from 1 to over 250 heartworms.
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Left untreated, heartworm disease is 100% fatal.
Why Heartworm Testing Is Essential
Even if your dog appears healthy, it may be carrying silent infections. Heartworms can cause irreversible damage before any outward symptoms show. That’s why regular heartworm testing is a cornerstone of preventive veterinary care.
Benefits of Heartworm Testing:
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Early detection helps avoid long-term damage.
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Ensures your dog is healthy before starting heartworm preventives (some medications can be dangerous if the dog is already infected).
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Helps monitor treatment success in previously infected dogs.
When to Test for Heartworms
The American Heartworm Society recommends annual heartworm testing for all dogs, even if they are on regular prevention. Puppies and newly adopted dogs follow a slightly different schedule.
Testing Guidelines:
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Puppies under 7 months: Can start prevention without a test, but should be tested at 6-7 months of age.
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Dogs over 7 months: Should be tested before starting prevention.
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After missed doses: If your dog misses even one dose of heartworm prevention, retesting in 6 months is crucial.
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Annually: All dogs should be tested every 12 months, regardless of previous results.
Types of Heartworm Tests for Dogs
There are two main types of heartworm tests used by veterinarians:
1. Antigen Test
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The most common and reliable method.
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Detects female adult heartworm proteins in the bloodstream.
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Results are typically available within minutes.
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Cannot detect infections younger than 6 months.
2. Microfilariae Test (Modified Knott’s Test)
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Confirms the presence of baby heartworms (microfilariae) in the blood.
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Often used alongside the antigen test to confirm diagnosis.
Some vets may use imaging (X-rays, echocardiograms) or blood panel tests if a dog is symptomatic or if complications are suspected.
What Do the Results Mean?
Negative Result:
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No signs of adult female heartworms.
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Prevention can continue or begin safely.
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Retest in 12 months.
Positive Result:
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Further testing needed to determine severity and microfilariae presence.
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Treatment plan will be developed, often involving:
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Pre-treatment antibiotics (e.g., doxycycline)
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Strict exercise restriction
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Adulticide therapy (e.g., melarsomine injections)
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Follow-up testing after treatment
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Heartworm Symptoms in Dogs (Don’t Wait for These)
While many dogs don’t show signs until the disease is advanced, here are symptoms to watch for:
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Persistent cough
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Fatigue after mild activity
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Weight loss
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Decreased appetite
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Labored breathing
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Swollen abdomen (due to fluid accumulation)
These signs require immediate veterinary attention.
Heartworm Prevention: The Best Medicine
Heartworm disease is expensive to treat and dangerous to your dog. But it’s also almost 100% preventable.
Common Preventive Options:
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Monthly chewables or topical medications (e.g., Heartgard, Advantage Multi)
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Six-month injection (e.g., ProHeart 6 or ProHeart 12)
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Some combo meds also protect against fleas, ticks, and intestinal parasites
Important: Never give your dog heartworm medication without first testing for infection, especially after a lapse in prevention.
FAQs About Heartworm Testing
Can my dog get heartworm from another dog?
No. Heartworm is not contagious; it requires a mosquito as a carrier.
Is heartworm common in my area?
Heartworm disease has been diagnosed in all 50 U.S. states, though it’s most common in warm, humid regions like the South and Gulf Coast.
How much does heartworm testing cost?
Typically ranges from $35–$75, depending on the vet and whether other tests are bundled.
Final Thoughts
Heartworm testing for dogs is not just a yearly formality—it’s a life-saving measure. With early detection, preventive care, and proper veterinary guidance, heartworm disease is entirely manageable and, most importantly, preventable.
If you’re unsure about your dog’s heartworm status or prevention plan, schedule a vet visit today. Your dog’s heart may depend on it.
