Diabetes mellitus is a metabolic disease caused by multiple etiologies and characterized by chronic hyperglycemia. Due to defective insulin secretion or/and action (insulin resistance), it leads to abnormal metabolism of carbohydrates, proteins, fats, water, electrolytes, etc., which can cause damage to multiple systems in the body. It leads to chronic progressive lesions of the heart, kidneys, brain, systemic blood vessels, nerves, eyes and other tissues, causing hypofunction and failure. Acute severe metabolic disorders, such as ketoacidosis, hyperglycemic hyperosmolar state, can occur during severe illness or stress. Diabetes decreases the quality of life, increases mortality and shortens life expectancy. Diabetes is classified into type 1 diabetes; type 2 diabetes; other specific types of diabetes; and gestational diabetes.