Hypoglycemia. Definition, clinical presentations, classification, and laboratory tests.

Hypoglycemia can be defined as the occurrence of a wide variety of symptoms in association with a plasma glucose concentration of 50 mg per dl or less. It may be asymptomatic, and the relief of the symptoms by administration of glucose is not sufficient to establish a diagnosis. Although the symptoms may be quite variable, they can be classified as adrenergic or neuroglycopenic. Hypothermia, hyperthermia, or localizing neurologic findings may be seen as a consequence of hypoglycemia. Severe, repeated episodes of hypoglycemia can cause a distal neuropathy that is primarily motor but can also have a sensory component. Hypoglycemia can be classified as fasting, reactive, surreptitious, or artifactual. Some causes of hypoglycemia are unique to infants and children. Underlying diseases such as liver disease, endocrine disease, or renal disease can be diagnosed by the characteristic physical findings and laboratory tests. Other causes of hypoglycemia can be identified by a variety of diagnostic tests involving measurement of glucose, insulin, C-peptide, and other related compounds.