Canine Heartworm Test

August 26 is National Dog Day, a perfect moment to celebrate the dogs we love—and protect their health with proactive care. One critical but often overlooked step in safeguarding your dog from disease is routine testing for heartworm. 

Heartworm disease, caused by Dirofilaria immitis, can remain hidden in a dog’s body for months. It targets the lungs, heart, and major blood vessels, often without obvious symptoms until the damage is severe. Testing is the only way to confirm your dog is truly protected. 

Why Testing Matters (Even for Dogs on Preventatives)

According to the 2024 guidelines from the American Heartworm Society (AHS), annual testing is recommended for all dogs over 7 months of age, even those consistently on preventatives. 

Here's why testing is essential:

  • Detects early-stage or missed infections 
  • Verifies your prevention plan is working 
  • Reduces the risk of silent disease progression 
  • Helps catch resistant strains that may evade standard medication 

Two Key Testing Methods

Veterinarians typically use a two-step diagnostic approach: 

1. Antigen Testing detects proteins released by adult female heartworms. It is nearly 100% specific but may not detect:

  • Early infections 
  • Infections with low worm counts
  • Male-only infections

AHS advises that positive antigen results should be confirmed either with a different test platform or by detecting circulating microfilaria.

2. Microfilaria Detection identifies the presence of larval heartworms (microfilariae) in the blood. It’s critical because it:

  • Validates antigen results
  • Flags the dog as a potential source of infection
  • Helps assess worm burden risk 

One effective method is filtration using a membrane filter, often a polycarbonate track-etch membrane, which provides good visibility under a microscope. 

Explore Studies Using Sterlitech PCTE Membranes for Microfilaria Detection

Multiple studies have utilized Sterlitech polycarbonate track-etch (PCTE) membranes in heartworm or parasite-related diagnostic methods, including microfilariae detection.

  • PMID: 36417831 – Exploration of the sensitivity to macrocyclic lactones in the canine heartworm (Dirofilaria immitis) in Australia using phenotypic and genotypic approaches 
  • PPR0394525 Preprint – The Use of Molecular Markers to Investive Possible Resistance to Heartworm Preventatives in Dirofilaria Immitis Samples from Heartworm Positive Dogs in Europe
  • PMID: 29143652 – Genetic profiles of ten Dirofilaria immitis isolates susceptible or resistant to macrocyclic lactone heartworm preventives
  • PMID: 25936435 – Macrocyclic lactone resistance in Dirofilaria immitis: Failure of heartworm preventives and investigation of genetic markers for resistance

Sources: 

American Heartworm Society Canine Guidelines: Prevention, Diagnosis, and Management of Heartworm (Dirofilaria immitis) Infection in Dogs. American Heartworm Society, Feb. 2025. https://d3ft8sckhnqim2.cloudfront.net/images/AHS_Canine_Guidelinesweb03FEB2025.pdf?1738626677