The diagnostic criteria of diabetes mellitus are: having symptoms of diabetes mellitus three more or less, satisfying random venous blood glucose ≥11.1mmol/L, fasting venous blood glucose ≥7.0mmol/L, OGTT 2 hours venous blood glucose ≥11.1mmol/L, and excluding temporary elevation of blood glucose caused by acute infection, trauma or other stressful situations, diabetes mellitus is diagnosed. There are also some prediagnostic criteria for diabetes, such as impaired fasting glucose when fasting glucose is ≥6.1mmol/L, but <7.0mmol/L. Diagnosed as impaired fasting glucose, when 2 hours postprandial glucose is ≥7.8mmol/L, but <11.1mmol/L. Diagnosed as impaired glucose tolerance.