Soggybadger. At this point a diagnosis of prediabetes is really nothing more than a warning that diabetes may occur and a call to action to modify any risk factors that are under your control, such as weight, diet and exercise. Your blood sugar is elevated but not to the level of diabetes. It causes no symptoms and poses no risk with diving. I would not even mark it on the medical statement.
Without knowing more, I wonder if the physical and emotional stress you have had this past year might not also be a factor in your elevated blood sugar and that you might expect an improvement with your levels as your renal status stabalizes.
So if the renal condition is not a factor at present, relax and go diving!