Diagnosis of FIV
Diagnosis of FIV requires an FIV antibody test. ELISA (enzyme-linked immunosorbent assay) is a simple test that can be done in most veterinary laboratories and clinics. The test involves examining the cat's blood for the presence of FIV antibodies. FIV antibodies are unique proteins that the immune system produces in response to FIV infection.
Test results are available within 10 to 20 minutes. False positives can occur, so all cats that test positive should be retested with a Western blot assay. The Western blot detects the presence of FIV-antibodies in the cat's blood using slightly different technology.
Sometimes the test result is inconclusive, in which case the cat should be tested again in 8 to 12 weeks. Diagnostic tests are unable to distinguish between cats that have been vaccinated against FIV and cats that are infected with the virus.
Some labs combine the FIV test with an FeLV (feline leukemia) test, since cats that are at risk for one are also at risk for the other.
Kittens born to FIV-positive cats often test positive due to maternal antibodies that they've ingested from their mother's milk. This doesn't mean that the kittens are infected, only that they have their mother's antibodies. The antibodies should disappear within a few months. Kittens under the age of 6 months that test positive should be retested when they are 8 to 12 months old.
A negative test result indicates that there are no detectable FIV antibodies in the cat's blood, which usually means that the cat doesn't have FIV. Antibodies don't usually develop until 8 to 12 weeks after the initial infection, which means the test result could be inaccurate if a cat was infected and tested within this 8 to 12 week period. FIV-negative cats that have been exposed to FIV-positive cats should be tested 8 to 12 weeks after exposure. Rarely, cats in the later stage of FIV infection may test negative because their immune systems have deteriorated and no longer produce antibodies.
A blood test may reveal the following abnormalities in FIV-positive cats:
- Anemia (abnormally low level of circulating red blood cells)
- Hypergammaglobulinemia (abnormally high level of gamma globulin, a type of antibody, in the blood)
- Lymphopenia (abnormally low level of lymphocytes in the blood)
- Neutropenia (abnormal decrease in the number of circulating neutrophils, a type of white blood cell)
The lifespan of FIV-infected cats is highly variable. More than 50 percent of FIV-infected cats remain asymptomatic for years. About 20 percent of FIV-infected cats die within 2 years of diagnosis (i.e., 4 to 6 years after infection). Cats in stage 3 of the disease usually die within a year.