[Hypoglycemia: clarification and etiology].

Spontaneous hypoglycemia occurs when the blood sugar falls below 50 mg/dl (2.8 mmol/l) and when neuroglycopenic symptoms appear. For clinical differential diagnosis separation of the hypoglycemias into fasting and postprandial hypoglycemias is suggested. Fasting hypoglycemia may be a symptom of insulinoma. The most important diagnostic tool in detecting insulinoma is still the simultaneous determination of glucose and insulin in plasma during fasting. A raised insulin level during hypoglycemia renders the presence of an insulinoma suspect; during fasting there is an inappropriate fall in blood glucose in relation to the course of the plasma insulin concentration, resulting in an increased insulin-glucose ratio. Recently determination of the fasting proinsulin level has been recommended as raised concentrations are pathognomonic for the presence of insulinoma. Evaluation of postprandial hypoglycemia is performed by oral glucose tolerance test with late glucose concentration determinations after three and four hours. This makes it possible to differentiate between reactive hypoglycemia in mild diabetes mellitus and "functional" reactive hypoglycemia, the most frequent cause of hypoglycemia.