Fasting for 12 hours to measure blood glucose may be inaccurate. The specific fasting time should be judged according to the patient’s own situation, for diabetic patients, fasting time is too long may lead to inaccurate measurement results, it is recommended that the fasting time control between 8-10 hours. Diabetic patients themselves already have abnormal blood glucose regulation, if fasting for a long time, it is easy to lead to hypoglycemia, resulting in rebound blood glucose increase, which leads to the measured blood glucose higher than the actual fasting blood glucose level. Before measuring fasting blood glucose, patients should maintain a healthy diet, do not deliberately reduce food intake or overeat, and strictly follow the doctor’s instructions for preparation.