Diabetes is a metabolic disorder characterized by chronic hyperglycemia caused by a variety of etiologies. Hyperglycemia is caused by defects in insulin secretion or action, or both. In addition to carbohydrates, there are abnormalities in protein and fat metabolism. Prolonged illness can cause multi-system damage, leading to chronic progressive lesions in the eyes, kidneys, nerves, heart, blood vessels and other tissues, causing functional defects and failure. Acute metabolic disorders such as ketoacidosis and hyperosmolar coma can occur when the disease is severe or stressful. Currently, diabetes mellitus is mainly categorized into four major types, namely, type 1 diabetes mellitus, type 2 diabetes mellitus, other special types and gestational diabetes mellitus.

(1) Type 1 diabetes mellitus

Patients with this type of diabetes mellitus have a tendency to ketoacidosis due to destruction of pancreatic islet cells, which causes an absolute lack of insulin, and contains two subtypes: immune-mediated diabetes mellitus and idiopathic diabetes mellitus.

Immune-mediated diabetes mellitus: Some patients of this type, especially children and adolescents, can have ketoacidosis as the first manifestation of the disease. In others, some patients have only mild fasting hyperglycemia, but it rapidly worsens in the presence of infection or other stressful situations, progressing to severe hyperglycemia and even ketoacidosis. In other patients (mostly adults) who can go for years without developing ketoacidosis, most patients need to rely on insulin therapy to survive.

Idiopathic diabetes mellitus: this group of patients is less frequent, with frequent ketoacidosis, mainly from certain races in Africa or Asia, and is highly hereditary.

(2) Type 2 diabetes

Most patients are obese, and obesity itself can cause varying degrees of insulin resistance. Some patients may have abnormal fat distribution, such as an increased distribution of abdominal or visceral fat, although they cannot be classified as obese by traditional weight criteria. Ketoacidosis rarely occurs spontaneously in this type of patient, but can be induced in emergency situations such as infections. Due to the slow development of hyperglycemia, many patients fail to attract sufficient attention in the early stages because of the absence of typical symptoms and fail to be diagnosed with diabetes for many years, yet they are at risk of developing macrovascular and microvascular lesions. The risk of this type of diabetes increases with age, obesity, and physical inactivity. It is more likely to occur in women with previous gestational diabetes and in patients with hypertension and dyslipidemia. The prevalence varies considerably between races/ethnicities. type 2 diabetes is more genetically susceptible than type 1 and is more complex.

(3) Other specialized types of diabetes

Some types of diabetes are known to be associated with single-gene defects in B-cell function, representative of adult-onset diabetes in young people. Genetic factors cause abnormal insulin action leading to the development of diabetes. Those caused by exocrine diseases of the pancreas, a range of endocrine disorders, drugs, or chemicals are actually secondary to diabetes.

(4) Gestational diabetes mellitus

After a pregnancy is established, if various degrees of reduced glucose tolerance or overt diabetes mellitus are detected, regardless of the need for insulin or dietary treatment only, and regardless of whether this condition persists after delivery, it can be considered gestational diabetes mellitus.