1999 WHO diagnostic criteria for diabetes: 1. Symptoms of diabetes (polyuria, polydipsia and unexplained weight loss) and random (any time after meal) plasma glucose ≥ 11.1 mmol/L (200 mg/dl); Liu Min, Center for Endocrine Genetic Metabolism, Beijing Children’s Hospital 2. or fasting (fasting for at least 8 hours) plasma glucose ≥ 7.0 mmol/L ( 126mg/dl); 3, or OGTT 2 hours plasma glucose ≥11.1mmol/L (200mg/dl) Impaired fasting glucose (IFG): is fasting plasma glucose ≥6.1mmol/L (110mg/dl), but <7.0 mmol/L (126mg/dl). Impaired glucose tolerance (IGT): is defined as OGTT 2-hour plasma glucose ≥7.8 mmol/L (140 mg/dl), but <11.1 mmol/L (200 mg/dl). Typing of diabetes mellitus: 1. Type 1 diabetes mellitus (destruction of pancreatic β-cells, resulting in absolute lack of insulin) There are 2 subtypes: immune-mediated and idiopathic 2. Type 2 diabetes mellitus (insulin resistance and/or secretion defects) 3. Other specific types of diabetes mellitus, with the following categories: (1) Genetic defects in β-cell function: MODY3, MODY1, MODY2, etc. (2) Genetic defects of insulin action: type A insulin resistance, leprechaun cat look-alike syndrome, adipose atrophy diabetes, etc. (3) Exocrine disease of the pancreas: pancreatitis, trauma or resection, tumor, cystic fibrosis, etc. (4) Endocrinopathies: acromegaly, Cushing's syndrome, pancreatic hyperglycemia, pheochromocytoma. (5) Drugs or chemical agents: niacin, adrenal glucocorticoids, thyroxine, α-adrenergic antagonists, β-adrenergic antagonists, thiazide diuretics, calcium channel blockers (mainly such as nifedipine), phenytoin sodium, pentamidine, the rodenticide Vacor (N-3 pyridinemethyl N-P nitrobenzyl urea) and α-interferon, etc. (6) Infections: congenital rubella and cytomegalovirus infections, etc. (7) Unusual types of immune-mediated diabetes: insulin autoimmune syndrome (insulin resistance), acanthosis nigricans II (insulin receptor antibodies, once called type B insulin resistance), "Stiff Man" syndrome, etc. (8) Other genetic syndromes with diabetes mellitus: Down syndrome, Friedreich's ataxia, Huntington's chorea, Klinefelter's syndrome, Laurence-Moon-Beidel syndrome, myotonic atrophy, porphyria, Prader-Willi syndrome, Turner syndrome Wolfram syndrome, etc. 4.Gestational diabetes