I thought that an HBa1c of 51 was in fact diabetic ! unless they have moved the goal posts again!
51 is considered a diabetic test results (I think the cut off is 48mmol/mol or above is diabetic, according to current uk diagnostic standards), but the closer to normal blood glucose levels, the better because it reduces our chance of diabetic complications.
So most of us are trying to keep our BG levels as low as possible, and preferably below diabetic levels.