Understanding Your Cat's FIV Test Results

Feline Immunodeficiency Virus, or FIV, affects the cat's immune system, making it difficult for them to naturally ward off infection. Frequently, infected cats show no signs or symptoms of infection for years. Most veterinarians suggest testing all cats for the disease for that reason.

Understanding the way the currently available FIV tests detect disease is important in interpreting results, and making decisions about your cat's health. The current in-house tests used by veterinarians, and even the more sophisticated Western Blot test used by diagnostic laboratories are all antibody tests. The body creates antibodies against specific viruses. Vaccines work by stimulating the production of antibodies so that when challenged with a true infection later on the immune system is ready to fight it off.

What a negative FIV test can mean

A negative FIV test can mean that the cat is not infected with the FIV virus. Most cats that test negative are truly not infected.

However, according to the Cornell University College of Veterinary Medicine, it can take from 8 to 12 weeks or more for an infected cat to produce enough antibodies for the tests to detect. Young kittens, or cats with possible exposure to FIV that test negative should be retested several months later to confirm.

Also, in very rare cases, an infected cat that is extremely debilitated from the disease many no longer be making antibodies to the infection if its immune system is no longer working well enough to do so.

What a positive FIV test can mean

A positive FIV test result can mean that the cat is infected with the FIV virus, regardless whether or not the cat is showing any symptoms of illness. Because the test detects the antibodies to the virus, and not the virus itself, there are other possibilities.

Kittens can receive antibodies from their mothers, but the actual FIV disease is not usually transferred from mother to kitten. These maternal antibodies will decline over time. Therefore, kittens that test positive for FIV before six months of age, should be retested after six moths to verify if the kitten is producing it's own antibodies, or if maternal antibodies were detected earlier.

There is a relatively new vaccine to protect against FIV infections. The available FIV tests cannot tell the difference between a cat with and FIV infection, and one that is producing vaccine stimulated antibodies. Vaccinated cats will test positive for FIV their whole life. This is especially important when considering a positive result from an adult cat with an unknown vaccination history. There is no test available today that can tell an FIV infected cat from a vaccinated one.

Additionally, according to the American Association of Feline Practitioners, the FIV vaccine works only about 82% of the time, at best. So even a vaccinated cat can also be infected with FIV, and test positive, but the test won't help determine if the positive result is from the vaccine or a true infection.

Hope for the future

Veterinarians are working on detecting FIV by a method called Polymerase chain reaction (PCR). This test detects some of the genetic material from the actual virus. At this time, unfortunately, the test produces a high amount of false results and is not considered reliable. For now we only have the antibody tests available, but a better, more specific test is actively being pursued by the veterinary community.