Holistic Care : Heartworm in Dogs : Types of Testing

We recommend testing your dog twice a year (six months apart) for heartworm infection, especially if you use a herbal protocol. If your dog is exposed for any reason, early detection allows for full recovery.

Serological test for antigens to adult heartworms: This is a test performed on a blood sample. It is the most widely used test because it detects antigens (proteins) produced by adult heartworms. As long as there are adult heartworms present, this test will be positive, even if there are no microfilaria/larvae present. Dogs with less than five adult heartworms will not have enough antigen to turn the test positive, so there may be some false negative results in early infections. Because the antigen detected is produced only by the female worm, a pure population of male heartworms will give a false negative, also. Therefore, there must be at least 5 female worms present for this most common test to be positive.

Blood test for microfilariae: A blood sample is examined under the microscope for the presence of microfilariae. If microfilariae are seen, the test is positive. The number of microfilariae seen gives a general indication of the severity of the infection. However, the microfilariae are seen in greater numbers in the summer months and in the evening, so these variations must be considered. Approximately 20% of dogs do not test positive even though they have heartworms because of an acquired immunity to this stage of the heartworm. Because of this, the antigen test is the preferred test. Also, there is another microfilarial parasite which is fairly common in dogs; on the blood smear, these can be hard to distinguish from heartworm microfilariae.

Blood chemistries: Complete blood counts and blood tests for kidney and liver function may give an indirect indication of the presence of heartworm disease. These tests are also performed on dogs diagnosed as heartworm-infected to determine the function of the dog's organs prior to treatment.

Radiographs (X-rays): A radiograph of a dog with heartworms will usually show heart enlargement and swelling of the large artery leading to the lungs from the heart. These signs are considered presumptive evidence of heartworm disease. Radiographs may also reveal the condition of the heart, lungs, and vessels. This information allows vets to predict an increased possibility of complications related to treatment.

Echocardiography (Sonogram): An echocardiogram allows vets to see into the heart chambers and even visualize the heartworms themselves. Although somewhat expensive, this procedure can diagnose heartworms when other tests fail.