HbA1c provides an index of average blood glucose levels over the past 8 –12 weeks and is a much better indicator of long term glycemic control as compared to blood and urinary glucose determinations. Since HbA1c reflects long term fluctuations in the blood glucose concentration, a diabetic patient who is recently under good control may still have a high concentration of HbA1c. Converse is true for a diabetic previously under good control but now poorly controlled.