Hi there, my name is Sophie and I am a registered veterinarian and I would like to try to help you today.
I'm sorry to hear about your poorly cat.
I think it would be best if we can chat this through together as I have a lot of things I'd like to ask you. I'll wait for you to come online.
Things I was interested in was if your cat is vaccinated? Have you had from a kitten? What does he eat? Is he an outdoor cat? Is he neutered? Has he had any medical problems in the past?
I'll wait to hear from you...
Ok so there is a possibility here of infectious disease as well as non-infectious disease. A blood test can show up marked changes in organs of the body etc but it doesn't show up all disease. In patients that are loosing weight further investigations may be needed. Has your vet discussed getting some x-rays or ultrasound scans of his belly to see if a cause for his weight loss can be found?
I would consider getting some more tests ran as these symptoms are really abnormal and worrying in a cat so young. You might want to discuss with your vet getting some screening x-rays and an ultrasound scan taken as well as some further blood tests for specific issues like B12/folate (which can show absorption problems in the gut) and pancreas problems (like a pancreas enzyme insufficiency).
Viral problems like FIP (feline infectious peritonitis) can also be a possibility and this is again a separate test.
Chat to your vet about getting some further tests as I feel from what you have told me this is likely the only way to get to the bottom of what is going on here, and the best way to treat the problem is to know what we are treating.
I hope this is helpful?
I hope it has been helpful. If it has been of any use at all please rate/accept my answer so justanswer can see I gave you useful info. I can see you popping in and out of the chat, I will be online for most of this evening (I have to pop out for an hour or so later) and you can reply to me any time. I'll switch into another mode to see if it is easier for you to reply. Don't worry chat isn't over!
All the best, SOphie