Thank you for this.
It is important that he has a blood test, even with the new measures, this is key for ensuring we have the right diagnosis.
It may be that he is not improving as there is something else going on.
High protein may indicate kidney issues but could also be seen with a urinary infection, high blood pressure, cushings disease etc
So, first of all, I would request a blood test.
If kidney failure is confirmed, we could try some anti nausea medicine and appetite stimulants.
Dehydration is the main concern so these should help him eat and keep hydrated.
If he won't eat the kidney diet, it's best to give him an alternative as it's more important he eats something, so offer his old favourites mixed with warm water to get him interested.