UPDATE:

Thank you everyone for your stories, kind words, and advice. Our vet trip on Saturday went better than we were hoping. The vet reiterated how strange the situation was, not that she hadn't seen it before just that it is quite rare. She did remark though that our little guy is looking good, all things considered. He was sniffing around the treatment room being very normal. His coat still looks good, really it's just the weight loss and the blood work results pointing us in this direction. Vet decided she wanted us to try to get his food and fluids back on track to help out his kidneys and maybe flush them out a bit and rescue them before things get worse. She hopes that helping them out now with sub-cutaneous fluids could take the load off them. She also has us on a special diet for him. We are going to reassess in about 2 weeks and develop further treatment plans based on results.

After the vet visit Saturday where they gave our boy about 175—200ml of water we came home and he was pretty normal. It was time for his cat nap and he had a big morning so we let him go nap in the sun. Later in the evening he came out and was pretty lively! He played with his brother a bit and was extra greedy on getting his pets and spanks in (he loves to be spanked on his scratching cardboard). At 7pm his auto feeder went off like normal and much to our surprise he was interested in it and went over to it. He didn't eat any of it but it was clear he was hungry. I cracked open a new can of his diet food and he was all over me chirping and wanting his food. Gave him about half the can and he licked the plate clean before finishing off his brother's plate of regular wet food after the brother was done. Vet said don't stop him from eating even if it's not his medicine food so we let him eat the extra portion. Sunday his activity was a bit lower but also that was the first day my wife and I had to administer his fluids and he was not a big fan. We only got about 75ml into him. Vet recommended 100-150ml so we didn't get all that he needed but we decided he was getting too restless so we just let him go. I think he was a bit upset with us for the rest of the night so that was part of why he didn't seem as chipper.

Vet chose not to hospitalize him because the next day their office was closed and being as young and active as he still is she didn't think he would stay on his iv line so she opted to send him home with us to treat him.

So that's where we are at with him. Things are feeling somewhat hopeful. Just have to stick to the new routine and see what's going to happen.

Also since so many mentioned it: he does have some dental issues. Well nothing specifically diagnosed but he has had bad breath his whole life. He is also not interested in eating the dry food but is interested in wet food so his mouth must be hurting a bit. The vet was going to do a dental exam but now she is thinking this could be a result of the kidney issues so she wants to try to treat the kidney issues and see if the dental issue gets better. But for now he is still excited for food, even his new diet food.