Hypoglycemia, condition characterized by an abnormally low level of sugar in the blood. Symptoms of hypoglycemia include weakness, shakiness, nervousness, anxiety, and faintness and actual fainting. Patients also may show marked personality changes and may seem intoxicated. Hypoglycemia is the result of hyperinsulinism, or an excess of insulin, due either to an overdose of insulin—in the case of persons with diabetes mellitus—or to the body's overproduction of insulin. Insulin is instrumental in regulating carbohydrate metabolism; when hyperinsulinism occurs, glucose is sharply depleted in the process of conversion to glycogen in the liver and muscles and to fat in the adipose tissues.
Hypoglycemia is a clinical syndrome with diverse causes in which low serum (or plasma) glucose concentrations lead to symptoms of sympathoadrenal activation and neuroglycopenia. This topic will review the clinical manifestations and provide a list of the causes of hypoglycemia.
Reactive, or functional, hypoglycemia—the most common type—occurs particularly among persons under emotional stress. It is also due to overproduction of insulin, commonly three to five hours after meals. Its symptoms are milder than those suffered by insulin-dependent diabetics, and it can be controlled by lowering carbohydrate intake. Because reactive hypoglycemia has many of the classical symptoms of depression or anxiety, it is often wrongly believed to be the cause of underlying psychological disorders. Even when this physical condition is properly diagnosed, it is most often found to be incidental to, rather than the direct cause of, the patient's symptoms.
There are no specific symptoms of hypoglycemia. Experimentally induced hypoglycemia causes symptoms of sympathoadrenal activation followed, if the serum glucose concentration falls further, by symptoms of neuroglycopenia. Hypoglycemia may be classified as fasting or postprandial, or insulin-mediated or non-insulin-mediated. The former classification has outlived its usefulness, because hypoglycemia that is only postprandial is very rare, and hypoglycemia that is primarily fasting can also occur postprandially. The insulin-based classification deals with pathogenesis but not cause. Hypoglycemia is an uncommon clinical problem in patients not being treated for diabetes mellitus. A prolonged supervised fast, which can last as long as 72 hours, is the oldest, best established and probably most reliable test for the evaluation of hypoglycemic disorders. However, this test is complicated and expensive and should be reserved for those patients in whom a reasonable diagnosis cannot be made by other means. In any case of hypoglycemia, including factitial hypoglycemia, the diagnosis can usually be established by appropriate blood tests at the time of hypoglycemia.
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