consolejockey

Carol, of Angels in Fur Cat Rescue, Simon’s former home, emailed me a few corrections about Feline Leukemia after reading my post. I know a lot of people who have cats and would find this information useful:

“False positives” on the in-office test for FeLV are not actually rare - they are common. Moreover, they are technically not “false”, as they accurately detect the presence of the virus in the cat’s blood. But a positive result on the in-office test does not mean the cat will necessarily develop a persistent infection with the virus. In fact, according to some veterinarians, 60% - 80% of cats with a healthy immune system who are exposed to the FeLV virus will develop antibodies that prevent the progression of the infection (for example, see: http://www.acfacats.com/felv.htm). That means the “false positive” rate on the ELISA test can be as high as 80%. (But again, I would argue that the term “false positive” is not really appropriate here.)

When Lucas had a positive test result, I made the error with him that I think Nancy also made with Simon, and that was not to either: (1) retest him immediately using a different test called an IFA test (indirect immunofluorescent antibody assay) that has to be sent to a veterinary diagnostic lab; or (2) retest him via the in-office ELISA test (enzyme-linked immunosorbent assay) in 6 - 8 weeks.

What I have learned since then is that an otherwise healthy adult cat who tests positive for FeLV via the in-office ELISA test should ALWAYS be retested in one or both of these two ways to confirm that the FeLV infection is persistent and not transient, because the majority of healthy adult cats who test positive using the ELISA test shortly after being exposed to the virus are able to mount an effective immune response against it. Weeks later, these cats will test as virus-free.

A very good pamphlet on feline leukemia that includes a description of the differences between the in-office ELISA test and the IFA test, and why both are needed, is available at http://www.vet.cornell.edu/fhc/brochures/felv.html.