Jenn, actually it is very difficult to tell the difference between FIP, which in the wet form produces abdominal/chest fluid, and a fluid-producing chest tumor caused by FeLV except by biopsy/necropsy. In addition, FeLV positive cats are more vulnerable to FIP than healthy cats. However, there is no definitive test for FIP like there is for leuk and FIV - the only way to diagnose it is by looking at symptoms, bloodwork, titer and biopsy/necropsy all together.
