Heartworm Disease in Dogs: Diagnosis

Heartworms in dogs are diagnosed in every state in the United States, but in some areasHeartworm Disease in Dogs: Diagnosis it is more prevalent than others. There are several different tests which may be used to diagnose heartworm in dogs. It is important to understand the different diagnostic tools as many dogs with heartworm infections have no clinical signs that owners may observe.

Heartworm in Dogs: Diagnosing Heartworm Infection in Dogs

Timing of heartworm testing is important as the lifecycle of the heartworm is complex.  The standard tests mentioned below should not be used prior to 7 months after possible infection transmission by a mosquito as adult worms and microfilaria will not be present prior to that time. Puppies less than 7 months do not need to be tested for the same reason.
Diagnosing heartworm infection in dogs requires a sample of blood.  The most common test is the antigen test, which detects a protein secreted by adult female heartworms.  The test can be negative in cases where there are a small number of worms, the worms present are immature females, or the worms are all males. However in most cases this test is very reliable, inexpensive and is performed at most veterinary hospitals so that results are available to owners within minutes.
The second type of test is also a blood test, but tests for the presence of microfilaria. Microfilaria are the offspring of adult female worms, and are the infective stage of heartworm disease which get taken in by the mosquito during a blood meal.  This test is not reliable by itself for diagnosing heartworm infections and is not recommended unless it is being used to confirm a positive antigen test.
Additional tests which may be performed by your vet include chest x-rays where changes in large blood vessels may be seen. The pulmonary arteries, where the adult worms live, can appear large and tortuous. Another test which may be used is an echocardiogram, or ultrasound of the heart. While heartworms can often be identified in an infected dog during an echocardiogram, it is most useful in determining the heart function prior to treatment for heartworms.
Once a diagnosis of heartworm infection is made and the heart function and overall health of the dog is determined, a treatment plan can be formed.

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Dr Jill Christofferson

Jill Christofferson, DVM is an experienced veterinary general practitioner. Her professional interests include ophthalmology, dentistry, and reproduction.

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