Renal issues

My boy began drinking a lot of water and producing excessive urine. Vet suspected renal failure, and he's had regular blood tests since June, but although the creatinine was high, the BUN remained in normal range. His tests are all similar numbers.

We visited a specialist who ran a contrast test to determine the level of kidney function, and he's only got 58% (although vet said they get 'concerned' at 75% loss of function).

Specialist said that there's no way to know how this happened (i.e., whether it's beginning CRF--he's only 6--or the result of some toxin--I suspect toy mice from China that he 'kills,' exposing a crumbly white substance that I'm sure he's ingested over the years that he's had these toys--his favorites).

Also there's no way to know whether this will be progressive or he can remain at this level for a while. Vet suggests testing every 3 months, but I'm tempted to leave him alone until he shows some further symptoms--e.g., loss of appetite or vomiting. The regular blood tests have been extremely stressful for him.

He's rejected the prescription foods I've tried and even some of the good non-prescription ones like Hi Tor and Wysong. I've done everything, including mixing in low sodium tuna water and sardine water (which he normally loves), but nothing has worked. Vet isn't concerned; says it's more important that he eat.

He eats 99% wet--but he wants his Fancy Feast (I've never been able to get him to eat any high-end food).

Anyone have any other suggestions?

Thanks for your helpful reply!

Neither vet has mentioned any 'renal support supplement,' but I will be sure to ask about it.

My sister also suggested forgetting about more blood tests until he shows some signs that the illness is progressing. She doesn't see him often but was visiting last week and remarked that he seemed perfectly 'normal' in the way he's behaving--i.e., playing, eating, sleeping, etc.

I've spent about $2,000 since mid-June getting to this point, so I'm not against spending money on my boy, but I also don't want to waste money and put him through stressful blood tests for no reason. He's probably had 6 blood panels since this started, and the numbers have been similar in every one of them.