I went in to the vet's office today and asked them. They told me things very similiar to what Catlady711 said. The vet tech said that a false positive is VERY rare, although not impossible. She also said that while the vaccines aren't 100% guaranteed to prevent infection they are very helpful. They've never had a cat that was properly vaccinated contract leukemia and they've had several challenged. Those were her exact words, the same ones Catlady used. I've never had one of mine retested. They've never mentioned that as a possibility even. I asked about Jose because he is about 6 weeks late with his shots, and they weren't too concerned. If it had been closer to a year, then they would have been. I have an appointment to take him in first thing tomorrow for his vaccinations. I would have taken him on time, except there was no way for me to get him without risking scaring Gary away for days or weeks and getting Gary vaccinated and neutered was my priority. I hope all goes well with the crew. That's all I can do at this point. I kept waking up last night afraid of all the possibilities that could happen with leukemia running through my whole crew.