High levels of glucose in blood of diabetic patients lead to attachment of glucose (glycosylation or glycation) to biological macromolecules like proteins, lipids, DNA and RNA. This impairs protein function and leads to diabetic complications as glycosylated proteins fail in their biological function resulting in diabetic neuropathy ( blindness), nephrotoxicity( kidney damage, glucose in urine), and leg ulcers. Attachment to Hemoglobin gives HbA1c which is a good marker for the glycemic status of the diabetic patient and indicates mean blood glucose levels during the past 3 months.

MBG is monitoring of blood glucose by using a glucose meter or glucose watch.

For details.

http://knol.google.com/k/diagnosis-of-diabetes#