All adult dogs are tested for Heartworm, the tricky part with the test follows:
It takes six months from the time a dog is bitten by a heartworm carrying mosquito to even have a Snap Antigen HW test show positive. If a dog was bitten in October 2008 by a HW carrying mosquito, they would not test positive until April 2009. Microfilarae (baby heartworms) does not show on an antigen test, only adult worms show. We would need to keep an adult dog in foster care for six months, do a HW test when they come in, keep them on monthly Ivermectin and have another test done six months later to be 100% guaranteed the dog is HW free. Your dog will have paperwork with the date of the HW test and the results, but there is no guarantee that a test in another few months will still show a negative result- A key factor is to keep your dog on monthly heartworm control and that will hopefully keep the microfilarae that did not show on the antigen test from developing into adult worms.