Do Dogs Need Blood Tests Before Taking Heartworm Pills?

Heartworm disease occurs when a mosquito infected with the Dirofilaria immitis parasite bites a dog and transfers the parasite. It can be fatal. Various veterinarian-prescribed monthly heartworm preventatives are available, though your buddy will need a quick blood test before he takes his first dose.


Heartworm Disease

A dog with heartworm disease first has baby heartworm larvae, microfilaria, swimming throughout his bloodstream. It takes six months for them to develop into adult heartworms and migrate into his heart and lungs. At this stage, an infected dog is at risk for heart failure and eventual death unless treatment occurs.

Microfilaria Test and Prevention

Every dog regardless of age, breed, location and size should be on a monthly heartworm preventative by age 6 months. Your veterinarian can help you decide which is right for your dog. Your veterinarian will want to do a quick blood test for microfilaria before starting prevetion -- if your dog is positive for microfilaria, a heartworm preventative could cause them to die off suddenly, increasing risk of blood clots and death. The test requires a small blood draw that's run through the centrifuge and inspected under a microscope. Further diagnostics are required if a dog is positive for microfilaria.

By Christina Stephens

About the Author
Christina Stephens is a writer from Portland, Ore. whose main areas of focus are pets and animals, travel and literature. A veterinary assistant, she taught English in South Korea and holds a BA in English with cum laude honors from Portland State University.