Diabetes mellitus is a group of metabolic diseases characterized by hyperglycemia due to defective insulin secretion and/or action. Long-term hyperglycemia causes damage to organs throughout the body, especially the eyes, kidneys, nerves, blood vessels and heart, leading to their dysfunction and functional failure. Causes: The result of long-term joint action of genetic factors and environmental factors, accounting for about 50% each. Main problem: Insufficient insulin or/and poor insulin action (resistance). Basic changes: increased blood glucose and other metabolic disorders. The diagnostic criteria for diabetes are: 1. diabetic symptoms + plasma glucose level at any time ≥ 11.1 mmol/l (200 mg/dl) 2. fasting plasma glucose (FPG) level ≥ 7.0 mmol/l (126 mg/dl) 3. 2hPG level ≥ 11.1 mmol/l (200 mg/dl) in oral glucose tolerance test (OGTT) ) The diagnostic criteria for diabetes mellitus in children are the same as those for adults. Explanation of diagnostic criteria: Diabetes diagnosis is based on fasting, any time or 2-hour blood glucose value in OGTT; fasting means no caloric intake for at least 8 hours; any time means any time of the day, regardless of the last meal time and food intake; OGTT (Oral Glucose Tolerance Test) is performed by taking blood in the morning on an empty stomach (after 8-14 hours of fasting) and drawing venous blood within 5 minutes after The test is performed by taking 75 grams of anhydrous glucose dissolved in 250-300 ml of water (82.5 grams if 1 molecule of crystalline glucose is used); no drinks, no aspiration, no strenuous exercise and no bed rest during the test; the blood is taken 30 minutes, 1 hour and 2 hours after taking the first sip of sugar water (for diagnostic purposes, only fasting and 2-hour venous blood can be taken); the daily carbohydrate intake for the 3 days before the test is not less than 1 hour. The daily carbohydrate intake should be at least 150 grams for 3 days before the test; stop using drugs that affect OGTT such as contraceptives, diuretics, β-adrenergic blockers, phenytoin, niacin for 3-7 days before the test, and no OGTT for those taking glucocorticoids. Diabetes diagnosis points to note: In the absence of hyperglycemic crisis, those whose blood glucose value reaches the diagnostic standard of diabetes at one time must be retested on another day according to one of the three criteria in the diagnostic standard. If the re-test does not reach the diagnostic standard of diabetes, it should be rechecked in the follow-up; temporary increase of blood glucose may occur in acute infection, trauma, circulation or other stressful conditions, which cannot be diagnosed as diabetes, and must be rechecked after the stress. Glycosylated hemoglobin (new diagnostic criteria), the significance of this test is to reflect the average blood glucose level in the past two to three months, more than 6.5% can be considered for the diagnosis of diabetes.