Whatever you do, ditch the dry food. Think about it. Cats (and people) with renal insufficiency need a lot of moisture, and dry food is the worst possible choice for a cat in this situation. The secret is to feed a really good source of protein and try and keep phosphorus levels down. Oral health is really important too as toxins released by diseased gums harm the kidneys. I'm a raw feeder which is really the best diet for all cats, including CRI sufferers, but realise that this kind of feeding isn't for everyone. Therefore I'd say your best bet is a really good quality wet food that's low on grain, high in animal protein, and low in phosphorus. (you may have to do a bit of research for this!) Keep an eye on your cat's teeth. Contrary to what a lot of vets (in the UK) advise, feeding a low-protein diet, particularly in the early stages of CRI is NOT beneficial and can lead to an insufficiency in protein intake, leading to the cat using up valuable muscle resources and literally wasting away.

Just over a year ago my cat was in the early stages of CRI. I switched her to a raw diet and her latest blood test came back completely normal, as did her specific gravity on her urine. She is however, on 2.5mg of Fortekor every day. She is strong and solid with fantastic muscle tone. The vet says although she can see she's an adult cat, she'd no way guess she was 16 years old and classed as "anziana" (elderly) as they say over here in Italy!!

Good luck with whichever route you take and feel free to PM me with any raw feeding questions if that's what you choose to do