Hypoglycemia (hypoglycæmia in the UK) is a medical term referring to a pathologic state produced by a lower than normal level of glucose in the blood. The term hypoglycemia literally means "under-sweet blood" (Gr. hypo-, glykys, haima). Hypoglycemia can produce a variety of symptoms and effects but the principal problems arise from an inadequate supply of glucose as fuel to the brain, resulting in impairment of function (neuroglycopenia). Derangements of function can range from vaguely "feeling bad" to coma, and (rarely) permanent brain damage or death. Hypoglycemia can arise from many causes and can occur at any age. The most common forms of moderate and severe hypoglycemia occur as a complication of treatment of diabetes mellitus with insulin or oral medications. Hypoglycemia is usually treated by the ingestion or administration of glucose, or foods digestible to glucose.
Endocrinologists (specialists in disorders of glucose metabolism) typically consider the following criteria (referred to as Whipple's triad) as proving that an individual's symptoms can be attributed to hypoglycemia:
However, not everyone has accepted these suggested diagnostic criteria, and even the level of glucose low enough to define hypoglycemia has been a source of controversy in several contexts. For many purposes, plasma glucose levels below 70 mg/dl or 3.9 mmol/L are considered hypoglycemic, but these issues are elaborated in more detail below.