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Mixed Feline Leukemia Test Results
Johari18 posted:
Hi, my 7 1/2 yr old cat recently became ill with a respiratory infection about 3 months ago, we discovered the illness after she started coughing/choking every night around 3AM, so after a few days we rushed her to the vet where she had a chest xray done, trachial wash ect. while doing all of these other tests she was also given a "snap" feline Leuk test and came up positive. We then did an IFA test and she came up negative. She was on all sorts of medicine to clear up the infection (Bronchial Dialators/steroids ect) but now she is doing much better and is on a daily inhaler for asthma. I just took her back to get retested for the feline leukemia and she again came up with the same results, so I am not sure what to think or do? my vet is now going to do a PCR test to "really" determine if she has it, I guess I am just wondering why she did not do this test to begin with? Any advice or opinion in the matter would be greatly appreciated. Thanks!
Sandy Willis, DVM, DACVIM responded:
HI Johari18,
These are all different tests for FeLV. They all test for the virus, not antibodies. The Snap ELISA test for FeLV is very sensitive and picks up some amount of the virus. It is positive early in the disease when the disease is in the circulation. But a significant number of cats will mount an immune response such that they "fight off" the virus and will not remain persistently infected. Persistently infected means that the virus is not in the cells, having infected the bone marrow. This state is what the IFA test measures. It can take up to three months from the time the snap test is positive for the IFA test to become positive, if the cat does not fight the virus off. In that case, the snap test become negative and the IFA remains negative.
This can be confusing even for veterinarians.
PCR is a relatively new test but might be helpful at this stage but I would still check an IFA test again in 3 months. Really the standard is to run the snap test and then confirm with additional tests, as your veterinarian has done.
There can rarely be false positives on the FELV snap and your veterinarian could also send the FELV ELISA in to their diagnostic laboratory to confirm their in house finding on the SNAP. The SNAP FELV test is rarely falsely negative, and thus we start with this test in the clinic.
I hope this helps somewhat. I encourage you to ask your veterinarian about the tests as well.
Dr,. Sandy


William Draper, DVM, better known as "Dr. Will," is a well-known small animal practitioner in the Atlanta, GA area. He grew up in Inglewood,...More

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