Full body CRPS here....Just had a lot of blood work done and my doctor says "Your kidneys look great!"
So, my experience is that the CRPS hasn't affected my kidneys while it has affected a lot of other parts of me.

I also have issues with urinating, but I had a serious spine injury which is what we believe to be the cause...damaged nerves in that area (saw a few Urologists to confirm this, and none felt it was related to my CRPS, which I would agree with, since my sex nerves are also impacted, and all this started at time of spine injury).