My kitten tested positive for FeLV. Our older cat tested negative, so she was vaccinated and they are kept separate. Should I do an IFA test in 2 months? If that is negative, is it safe to re-introduce the 2 cats? Does a negative result after a positive mean that she can no longer transmit the disease?

I am sorry for your dilemma.  I would keep these cats strictly isolated.  I would repeat the FeLV snap test and perform a FeLV IFA in 2 months.  If either one remains/is positive then your kitten could still expose your other cat. 25% of these cats convert to negative on both tests (safe), 25% become positive on both tests (typically soccumb to the virus and more common in kittens), and 50% remain discordant (where the results of the 2 tests are different and the patient may never become ill). Unfortunately, these discordant cats are still potentially contagious.  Good luck.

Christine Simon D.V.M.