*If* this is CKD (I don't like the term CRF, F sounds so .... well, final!), he's likely in Stage 2 according to the IRIS staging charts. See
http://www.iris-kidney.com/pdf/IRIS%20A5%20Cards.pdf slides 3 and 4 for a quick overview (they have staging for dogs in there too, in slides 1 and 2 - skip those or you'll give yourself a big fright, like I did).
Here's a more extensive IRIS staging document:
http://www.iris-kidney.com/pdf/IRIS%202 ... %20CKD.pdf I've read it once, now I'm lazy and just scroll to slide 5 for the flowchart. Notice they start with creatinine, but they also sub-stage by urine protein/creatinine ratio and BP. Has he had those measured? If he's spilling protein, the approach is a little different - you'll add benazepril into the mix, and that has to be given apart from the binder.
I know what is generally recommended in managing CKD, but I hesitate to comment much here because of his complicated history - the pyelonephritis and Cushing's and hyper-t, among others. (Did he get another T4 rerun yet?) And that low RBC and Hemoglobin - at Stage 2, or even early Stage 3 - has me stumped; we haven't had to deal with that yet. Jess or Jojo or Dr Lisa may be the best folks to seek thoughts from. He's had extensive x-rays and ultrasounds, right? No kidney stones, just recurring pyelonephritis? Maybe send Jess a PM and link to this condo for her thoughts? (Add in all the values and ref ranges you have available - CBC, chem, T4, eta: urinalysis, culture, if done, etc - if you do, so they can get the whole picture).
Speaking of renal food, if you want to try any, the only one that's low enough in carbs for a sugarkitty is the Royal Canin line. I'm not for or against renal diets; it's a decision you'll have to arrive at yourself. There is an interesting thread on the old Think Tank about it; I can get you the link if you'd like to read it, after this all sinks in.