It may require a second blood sample if you want more certainty. Do ask your vet. Don't be afraid to tell him you've done your own research. If second sample is suggested then you can decide based on how stressful that is for him (Panda not the vet). Is there some different course you could be taking if it's something else? Or do you just want certainty? He sounds like he's doing well now that the infection has cleared, if a little baldy! But you know him best
Ask everyone. Ring a second vet (offer to pay for a phone consult and get copies of his records over to the 2nd. Make an exam video. Vets have internet too.) I once took a cat to 5 different vets before one could tell me what was wrong with her.
Hang in there and just love the little guy.