For normal people, the normal standard of 2 hours postprandial blood glucose is 4.4~7.8mmol/L. The normal fasting blood glucose value is 3.9~6.1mmol/L. If the patient has the clinical symptoms of diabetes mellitus, he/she may have more than one blood glucose. Normal fasting blood glucose value is 3.9~6.1mmol/L. If the patient has the clinical symptoms of diabetes mellitus three more and one less (more drinking, more eating, more urination, weight loss), plus the 2-hour postprandial blood glucose is more than 11.1mmol/L suggests diabetes mellitus. If the 2-hour postprandial blood glucose is between 7.8 and 11.1 mmol/L, impaired glucose tolerance is suggested. The 2-hour postprandial blood glucose is particularly critical in the diagnosis and treatment of diabetes. For people suspected of having diabetes, it is important to check both fasting and 2-hour postprandial blood glucose, and to do a glucose tolerance test if necessary to avoid missing the diagnosis of diabetes. If abnormal blood glucose is detected, an early visit to an endocrinologist is recommended for a definitive diagnosis.