Glycated hemoglobin is the product of glycosylation of glucose in the blood with hemoglobin in the red blood cells. The life span of hemoglobin is 120 days, so glycated hemoglobin is an indicator of the average blood glucose level over the past 2-3 months. Glycosylated hemoglobin is affected by anemia and blood glucose levels. The normal value of glycosylated hemoglobin in a normal person is 4%-6%. If the assay is reliable, diabetes may be present when glycosylated hemoglobin is greater than 6.5%, and fasting and postprandial glucose needs to be rechecked to determine this. The criteria for good glycemic control in diabetic patients are fasting blood glucose below 7.0 mmol/L, non-fasting blood glucose below 10.0 mmol/L and glycated hemoglobin below 7%. If the diabetic patient is older, has combined acute and chronic complications or has limited life expectancy, frequent hypoglycemia and poor self-monitoring management ability, glycosylated hemoglobin can be relaxed appropriately to less than 8%.