We got the second set of blood tests done on him yesterday. Thankfully he showed some improvement. The biggest change has been his demeanor over the last 36 hours or so. He's back to acting like a normal, if tired, kitty. He's no longer acting like a sick cat.
We've brought him home and will continue to treat him with sub-cu fluids and other medications for the time being. We'll get his blood tested again next week and see if he has continued to improve.
Overall, the outlook has improved immensely.
Here's an old pic of him: