Classification and subtypes of diabetes: The difference between type 1 and type 2 diabetes

Diabetes mellitus is a group of metabolic diseases characterized by chronically elevated blood glucose (blood sugar) levels, caused by defects in insulin secretion and/or action. Long-term disorders of carbohydrate, fat, and protein metabolism can cause multi-system damage, leading to chronic progressive lesions in tissues and organs such as the eyes, kidneys, nerves, heart, and blood vessels. Currently, the commonly used diagnostic criteria for diabetes in my country are the World Health Organization (WHO) 1999 criteria (Tables 4 and 5).

Table 4. Classification of Glucose Metabolism | Classification of Glucose Metabolism | Fasting Blood Glucose (mmol/L) | 2-hour Postprandial Blood Glucose (mmol/L) | | :--- | :--- | :--- | | Normal Blood Glucose | <6.1 | <7.8 | | Impaired Fasting Glucose (IFG) | 6.1～7.0 (excluding 7.0) | <7.8 | | Impaired Glucose Tolerance (IGT) | <6.1 | 7.8～11.1 (excluding 11.1) | | Diabetes Mellitus (DM) | ≥7.0 | ≥11.1 |

Table 5 Diagnostic Criteria for Diabetes Mellitus | Diagnostic Conditions | Venous Plasma Glucose Level mmol/L (mg/dl) | | :--- | :--- | | 1. Diabetes symptoms plus: | | | (1) Random blood glucose | ≥11.1 (200) | | (2) Fasting blood glucose | ≥7.0 (126) | | (3) 2-hour post-glucose load blood glucose | ≥11.1 (200) | | 2. For asymptomatic individuals, blood glucose should be measured again on another day to confirm the diagnosis | |

According to the World Health Organization's 1999 diagnostic criteria for diabetes, diabetes is classified into the following main types: ① Type 1 diabetes; ② Type 2 diabetes; ③ Other special types of diabetes; ④ Gestational diabetes mellitus (GDM). (1) Type 1 diabetes: mainly due to the patient's own immune system, which destroys pancreatic beta cells, leading to an absolute lack of insulin secretion and severe glucose metabolism disorder. Type 1 diabetes patients are generally under 30 years old. Their pancreatic beta cells are destroyed by more than 80%, resulting in an absolute lack of insulin and a tendency to develop ketosis. They must use insulin for life. (2) Type 2 diabetes: the cause is insufficient insulin secretion by pancreatic beta cells and tissue insensitivity to insulin (insulin resistance). It is the most common type of diabetes, accounting for more than 90% of diabetes patients. The onset of type 2 diabetes is related to genetic factors and environmental factors (overeating, obesity, and reduced physical activity). Most type 2 diabetes patients are adults, and the vast majority of patients are overweight or obese. They are mainly characterized by insulin resistance, and early symptoms are not obvious. Dietary therapy and oral hypoglycemic drugs are often effective. Acute complications of diabetes include diabetic ketoacidosis coma, diabetic nonketotic hyperosmolar coma, diabetic lactic acidosis, and diabetic hypoglycemic coma. Chronic complications of diabetes are mainly divided into microvascular and macrovascular complications. Microvascular complications mainly include diabetic retinopathy and diabetic nephropathy. Macrovascular complications refer to the early stages of diabetes, such as hyperinsulinemia, hypertension, and lipid metabolism disorders, as well as hyperglycemia after the onset of the disease, which are the causes of atherosclerosis in large and medium-sized arteries. Other complications include diabetic neuropathy and various infectious diseases. Diabetic ketoacidosis (DKA) is the most common acute and serious complication of diabetes, occurring mostly in patients with type 1 diabetes. Several days before onset, patients often experience worsening of polydipsia, polyuria, severe fatigue, weakness, nausea, and vomiting. As the condition worsens, the "three highs and one low" (polyuria, polydipsia, polyphagia, and weight loss) become significantly more pronounced, consciousness deteriorates, and the patient gradually enters a coma, accompanied by dehydration, shallow and rapid breathing, and a rotten apple odor. Nonketotic hyperosmolar diabetic coma is more common in the elderly. The causes of this disease include: infection, trauma, surgery, acute pancreatitis and other stressful conditions; excessive water loss. The onset of the disease is relatively slow, and the main manifestations are the prominent symptoms of diabetes mellitus, namely polyuria, polydipsia, polyphagia and weight loss.