A 2-hour postprandial blood glucose of 12.8 mmol/L can be diagnosed as diabetes if it is accompanied by the typical diabetic symptoms of polydipsia, polyphagia, polyuria, and weight loss, which is a more serious condition that requires prompt treatment. The diagnostic criteria for diabetes are fasting blood glucose greater than or equal to 7.0mmol/L, or 2 hours after meal blood glucose greater than or equal to 11.1mmol/L, or random blood glucose greater than or equal to 11.1mmol/L, and accompanied by typical symptoms of diabetes such as polydipsia, polyphagia, polyuria and weight loss. If the 2-hour postprandial blood glucose is measured to be 12.8 mmol/L, and the symptoms of diabetes mellitus of three more and one less are also present, diabetes mellitus can be diagnosed and needs to be actively treated. If there is only a 2-hour postprandial blood glucose of 12.8 mmol/L, but there are no typical symptoms of diabetes mellitus, you can retest on another day to make sure again. If you have a 2-hour postprandial blood glucose of 12.8mmol/L with abnormal symptoms, it is recommended that you go to the hospital to complete the relevant tests, such as glucose tolerance and glycated hemoglobin, etc., to determine whether you have diabetes, and then consult and treat you under the guidance of your doctor in a timely manner, so as to avoid delays in your condition.