Blood glucose is, as the name implies, the glucose in the blood. There are various clinical subdivisions, such as venous plasma glucose, whole blood glucose, and peripheral or capillary glucose. Venous plasma glucose is generally considered to be the primary indicator of observation. Physiologically, blood glucose is the body’s main energy supplier, together with fat and protein, to ensure the body’s energy needs. Blood glucose is required to provide almost all of the body’s energy needs. Only when blood glucose remains stable can the normal energy metabolism of the body be ensured. Blood glucose in the human body changes all the time and fluctuates significantly with meals and various activities, rather than being a constant value as one might imagine. Under physiological conditions, such as eating or emotional stress, blood glucose will rise, and under pathological conditions, such as diabetes and hyperthyroidism, blood glucose will also rise. When blood glucose is needed for energy supply, blood glucose is low or cannot play a corresponding role, or when blood glucose appears abnormally high under normal conditions, it will cause various diseases and produce different adverse effects. It is considered normal to have blood glucose of 3.9-6.1 mmol/L in fasting and less than 7.8 mmol/L 2 hours after meal, and when it is below or above this range, it is important to pay attention to whether there are various diseases or special conditions.