Has he ever gotten into ticks, katts? Some of the tick-borne diseases can mess up WBC and platelet counts and they can be really hard on the organs...especially if the disease becomes chronic. At least that happens in dogs--not sure what the symptoms might be in cats.
Hope you can find some answers soon!
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."