Randi - this may be grasping at straws at this stage, but I thought I'd throw it out there for what it's worth.

A few years ago, Myndi had a GI bleed, and her red blood count was so low, that her vet was truly amazed that she was still alive, let alone still being able to walk. Along with the meds for her ulcer, she was put on a very potent vitamin supplement that was high in iron, and I was told to give her as much liver that she could/would eat. After 2 weeks when she went back for a followup visit (which I truly didn't expect her to live long enough to make), all her blood values were normal and right where they should be. She wasn't a young dog when this happened either - she was 14 and considered a senior. This might be worth a mention to the vet, but I'm no doctor, so I don't know if anything like this would work for Fister.

Still hoping for a miracle for your dear boy.