What is the reference range for Creatinine for your lab? Is her phosphorus mid normal or high end normal?
I'm sure you've looked this up already but Creatinine is a waste product of the muscles that is excreted by the kidneys, as a result some large muscular cats have naturally higher levels, elevated levels can indicate kidney impairment, or pancreatitis. Creatinine presents a more accurate picture of the kidney function than BUN does because Creatinine is not as affected by diet, exercise or dehydration - it also means it can be a little more difficult to get it to drop than BUN.
http://www.felinecrf.org/diagnosis.htm#creatinine
I prefer not to fast kitties prior to testing, and my vet has never mentioned fasting, but I do try to have the tests run roughly the same time of day as the numbers do fluctuate all the time throughout the day.
As for raw diet, I know you feed prey model so this may not work for you
Duffy can not handle any bone, not even ground bone, so I feed
Feline Futures TC Instinct Plus Chicken Liver (bottom of the list) with ground chicken. There is a formula without the liver, TC Instincts, so you can add your own organ meat, and you do not have to use ground meat you can use chunks, I happened to find a butcher shop who has a lot of raw feeding customers & they sell frozen ground chicken in bricks.
Instructions for regular receipe
Instructions for reduced protein receipe I've not tried this as I suspect Duffy wouldn't eat it for long
Duffy's homeopath put her on
Azodyl to reduce both BUN & Cre 1st Dec and I started the FFTCIPCL fully in mid Dec 09 & both her numbers have dropped nicely