The manifestations of hypoglycemia evolve in a characteristic pattern. Mild hypoglycemia—for example, blood glucose concentrations less than 55 mg per 100 ml (3 mmol/l)—causes hunger, fatigue, tremour, rapid pulse, and anxiety. These symptoms are known as sympathoadrenal symptoms because they are caused by activation of the sympathetic nervous system, including the adrenal medulla. Activation of the sympathetic nervous system increases blood glucose concentrations by mobilizing liver glycogen, which is the principal storage form of carbohydrate in liver and muscle. More severe hypoglycemia—for example, blood glucose concentrations less than 45 mg per 100 ml (2.5 mmol/l)—causes blurred vision, impaired thinking and consciousness, confusion, seizures, and coma. These symptoms are known as neuroglycopenic symptoms because they are indicative of glucose deprivation in the brain. Sympathoadrenal symptoms and neuroglycopenic symptoms are nonspecific and should be attributed to hypoglycemia only when relieved by either oral or intravenous administration of glucose