A 2-hour postprandial blood glucose of 21 is usually defined as a 2-hour postprandial blood glucose of 21 mmol/L, which is above the normal range and is usually considered severe, with poor glycemic control. Diabetic patients with a 2-hour postprandial blood glucose of 21 mmol/L are considered to have poor diabetic glycemic control. Long-term poor glycemic control may lead to complications, including acute complications (diabetic ketoacidosis and hyperosmolar hyperglycemic syndrome, etc.) and chronic complications (aortic atherosclerosis, microarteriosclerosis and diabetic peripheral neuropathy, etc.). The occurrence of these complications may affect the quality of life and life expectancy of diabetic patients. Therefore, it is recommended that people with a 2-hour postprandial blood glucose of 21 mmol/L consult an endocrinologist for treatment under the supervision of a physician.