<prompt> Diabetes control is best monitored by -Serum glucosePost prandial blood glucoseHbA1cHbA2c  <response>: Measurement of glycated hemoglobin HbA1c is the standard method for assessing long-term glycemic control. When plasma glucose is consistently elevated, there is an increase in nonenzymatic glycation of hemoglobin. This alteration reflects the glycemic history over the previous 2-3 months, because erythrocytes have an average life span of 120 days glycemic level in the preceding month contributes about 50 to the HbA1c value. Measurement of HbA1c at the point of care allows for more rapid feedback and may therefore assist in adjustment of therapy. A rise of 1 in HbA1c corresponds to an approx average increase of 2 mmolL 36 mgdL in blood glucose. Reference : page 2410 Harrisons Principles of Internal Medicine 19th edition 