Some thoughts that might be of interest to others: my cat had a high
creatine level (and BUN) indicative of kindey problems (renal
failure). the main issue in treatmetn is changing diet...the standard
advise is to move to soething like Hills KD. My cat, like so many cats
it seems, would not eat this...she lost weight, would just not eat.
Finally, my husband did some research on other, low-protein deits and
found something called Hi-Tor Neo Diet, which contians more protein
than KD but lots less than regular quality cat food (like Science
Diet). My cat would eat this...the short version is that when we gave
her this, she starting eating again...and her creatin and BUN levels
within a few months fell back to NORMAL range, which we took to be
a minor miracle. So, I would urge anyone with similar problems to
consider the Hi-Tor Neo for cats. It saved my cat's life.

note: I have zero relationship with the company. I'm just a satisifed
customer.