Definition Diabetes mellitus (DM) is a metabolic disorder characterized by chronic hyperglycemia caused by multiple etiologies. Hyperglycemia is caused by a defect in insulin secretion or action, or both. In addition to carbohydrates, there are also abnormal protein and fat metabolism. Prolonged disease can cause multisystem damage, leading to chronic progressive lesions of the eye, kidney, nerves, heart, blood vessels and other tissues, causing functional defects or failure. Etiology and Epidemiology The etiology of diabetes has not been fully elucidated. The etiology of different types of diabetes varies. Broadly speaking, the causes of all types of diabetes can be summarized as genetic and environmental factors. Diabetes is a common and prevalent disease, and its prevalence is rapidly increasing with the improvement of people’s standard of living, aging population, lifestyle changes, and advances in diagnostic techniques. Recent studies show that the prevalence of diabetes among people older than 20 years of age is 9.7%, which means that 92.4 million adults in China have diabetes. The concern is that at least 25-50% of people with diabetes are undiagnosed, and less than 1/3 of those diagnosed are under ideal control. According to the international classification criteria proposed by the American Diabetes Association (ADA), diabetes mellitus is etiologically classified into four categories: 1) Type 1 diabetes mellitus (beta cell destruction, usually resulting in absolute insulin deficiency) 2) Type 2 diabetes mellitus (from insulin resistance with relative insulin deficiency to insulin deficiency with insulin resistance) 3) Gestational diabetes mellitus (GDM) 4) Other specific types Diabetes mellitus (not many patients, many types) Symptoms (clinical manifestations) The clinical manifestations of diabetes mellitus are important clues for the diagnosis of diabetes mellitus, mainly including: 1.”three more and one less”: namely, polyuria, polyphagia, polyphagia, physical strength and weight loss; 2.preprandial hypoglycemia: caused by insulin secretion and blood sugar asynchrony; 3.skin itching: caused by hyperglycemia Stimulation of nerve endings caused; 4, vision loss: can be caused by blood sugar fluctuations, cataracts, fundus bleeding and other causes.