A. Very rarely, a dog can have a heartworm infection and still test negative on an antigen test since the antigen tested for is produced only by the female worms. If the heartworms were not fully mature, or there were only male worms present, the antigen test result in infected animals would be falsely negative. This means the test result is negative when the animal is really infected.
An antibody test will be positive even if only one male worm is present. But this test has a downfall, too. Although it is very good at giving positive results when an infection is present, a positive antibody test just means the animal has been exposed to heartworms, but may or may not currently have heartworm disease. A negative antibody test means the animal has never been exposed to heartworms.
If they are actually seeing the heartworms via ultrasound, I would follow precautions by restricting exercise. This requirement might be difficult to adhere to, especially if your dog is accustomed to being active. But your dogâ€™s normal physical activities must be restricted as soon as the diagnosis is confirmed, because physical exertion increases the rate at which the heartworms cause damage in the heart and lungs. The more severe the symptoms, the less activity your dog should have. And the diagnosis should be confirmed. Once a dog tests positive on an antigen test, the diagnosis should be confirmed with an additionalâ€”and differentâ€”test. Because the treatment regimen for heartworm is both expensive and complex, your veterinarian will want to be absolutely sure that treatment is necessary.
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