I don't know why the OGTT isn't part of the standard neuropathy diagnostic ritual. It certainly seems that there's ample evidence indicating it should be.

This is what the Cleveland Clinic says on one of its webpages:

http://www.clevelandclinicmeded.com/...hy/Default.htm

"It is important to screen patients for diabetes mellitus. In the past, a fasting blood sugar or hemoglobin A1c, or both, was often performed, but recent reports suggest that impaired glucose tolerance detected on a glucose tolerance test might provide more meaningful information regarding diabetes as a potential cause for polyneuropathy."