Having only one kidney is not a "kidney disease" as long as the kidney is working well. I have been told that some doctors may simply look at your test numbers, compare them to charts for "average" (TWO-kidney) people and casually declare "stage 3 disease". Other doctors will look at your entire health picture, take into consideration that YOU have only one kidney, and THEN determine if you have "stage 3 disease" or if this is your a"new normal". So it would be wise, I think, to ask further questions. Does your doctor have experience in treating living kidney donors? That can make a difference.
Fr. Pat