My understanding of the pre-diabetes to diabetes shift is that in otherwise healthy people, with no external or pharmaceutical interferants, such as steroids, the percentage shift from pre-diabetes to frank diabetes is c30%. This was from an Australian academic paper, but I don't, unfortunately have time this morning to search it out. Clearly any prediabetes levels should be taken as a warning bell, and where appropriate, steps taken to trim that number back.
It could be the renal team just want to ensure the donor body isn't rattling over the diabetes line as that could throw a whole new set of questions into the melting pot.
@Amandlaz - you are doing the right things to shift your HbA1c in the right description. Don't get hung up on the 32 number quoted, as finger prick testing can miss both highs and lows, but it certainly sounds like you are giving it your best shot to get into your best shape for the challenge. I really do wish you and your son the best of fortunes with this. It's a courageous thing for you both to undertake.