I recently had my cat Max test positive for FIV. From what I know, false positives are not uncommon, and a false negative is much more reliable than a false positive. That's been the consensus everywhere I have looked and asked. If they test positive on the ELISA, do the blood test. Re-check, if they are positive as kittens, as it could be false. I'm hoping that when we bring our Max back in at 6 months for his neuter, his is positive as well.