Wow....I just saw this thread. I am highly concerned that your vet may not be on the top of his game. Is there any way you can post the entire lab? Labs are pieces of the puzzle that need to be put together. I would like to take a look at the other values.
My first thing I would do it to start sub-q fluids. I would really pay attention to his diet. Pellets are the primary reason proteins are high....and if they are high for extended periods of time, stress to the kidneys will result. The thing to watch for when doing the fluids with a possible kidney issue is edema in the chest cavity. Was a titer for EC performed with the labs? If not, I certainly suggest doing one. Spores from EC causes all sorts of renal issues. I would also like to see some rads to see if there is any calcification in the bladder and/or kidneys. I highly suspect that your rabbit might have an elevated glucose level too.
Just a thought about calcium levels. While it is true that rabbits metabolize calcium in an unusual manner, there is a concern called Metabolic Bone Disease. It is always a nutrtional issue. MBD is a combination of factors involving calcium/phosphorus ratios and access to Vitamins D2 & D3. The D vitamins are attainable thru only two methods.....exposure to direct unfiltered sunlight or supplements. MBD can present as all sorts of problems including weight loss, fur loss, dental issues in which the teeth can migrate or even fall outand in extreme cases, severe seizures as well as other clinical presentations. Calcium is a vital part of a healthy body....but like all other elements, in proper levels.
Has a full urinalysis been performed? If a kidney issue is in play, we need to know what is in that urine. The information provided by the blood labs and the urinalysis should bring things more into focus. And again, if possible, either post the labs or send them directly to me....my e-mail is listed.
In the meantime, make sure hydration is good....and remember that leafy greens provide a lot of hydration. You might want to add some canned pumpkin to his diet (NOT pie filling....canned pumpkin_ This is highly nutritious and many rabbits will eat it willingly. If you have some high quality alfalfa hay available, crush the leaves into as small a pieces as you can and mix in with the pumpkin. Feed a variety of high nutritional greens such as kale, dandelion greens and carrot tops. I would have no problem with your rabbit receiving an injection of B Comp ( a vitamin) as this usually helps to stimulate their appetite and makes them generally feel better.
Try to get those labs for us.
Randy