What is a Heartworm test?

            A heartworm test is a blood test used to detect the presence of heartworms in your pet.  A small blood sample is needed for heartworm testing. Dogs under 6 months of age do not have to be tested prior to starting heartworm prevention. Dogs over 6 months of age must be tested prior to starting or re-starting heartworm prevention. Dogs that are infected with heartworms can have severe reactions, including death, if heartworm prevention is given.

There are actually two types of heartworm tests.

            An "Occult" heartworm test is the most common test done and is usually done every year. It is testing for the proteins that naturally come off the skin of the adult worm that lives in a dog's heart. At least half a dozen worms are needed for this test to be positive. This test will be negative if only a few worms are present.

            A "Filter" heartworm test is needed if any heartworm prevention has been missed. This "filter" test is testing for Microfilaria, or the larva that are produced by the worms in the heart. This test can be positive even if the occult test is negative since you only need two heartworms to make Microfilaria.