Glycated hemoglobin can be checked to find out the average level of blood glucose in the last two to three months, and can also identify diabetes mellitus. Fasting blood glucose and 2-hour postprandial blood glucose can only reflect blood glucose at a certain point and are highly influenced by dietary factors. Glycated hemoglobin reflects the average level of blood glucose in the last two to three months and helps to assess the overall glycemic control of diabetic patients. Glycated hemoglobin is recommended to be controlled within 7.0% in diabetic patients. For those with longer disease duration, history of cardiovascular disease, or very high risk of cardiovascular disease, glycated hemoglobin should be controlled to <8.0%. Elevated blood glucose in stressful situations, such as acute infections, pancreatic disease, cerebral hemorrhage, etc., will normalize after the stressor is removed. Stress-induced elevated blood glucose with normal glycosylated hemoglobin can be used to identify diabetes. Diabetic patients should not only monitor fasting blood glucose, two hours after meal blood glucose, but also recheck glycated hemoglobin every three months. The occurrence of uncomfortable symptoms, timely medical treatment.