Kathryn...I lost my ten week old kitten yesterday to the exact same thing. I an devastated, as is my other cat, and feel guilty that he could not be saved. I was given two possible explanations: 1) bone marrow leukemia, which gives a false negative in the regular test or 2) a form of the herpes virus which can shut down the bone marrow. Either is incurable, and he would have had to suffer through many tests only to come to the same result. I know you went through this a few years ago now, but i can still feel your pain..i made the decision to help him rest and be at peace, as much as it killed me to do. Thank you for posting your journey with Timmy. It helped a lot.