Functional hypoglycemia: facts and fancies.

When blood glucose decreases below a given threshold, symptoms of cerebral dysfunction and/or adrenergic hyperactivity appear. If this occurs postprandially in otherwise normal subjects, a diagnosis of reactive or functional hypoglycemia may be proposed. However, these symptoms are not specific, and they should coincide with low blood glucose values and be rapidly relieved by glucose ingestion before a diagnosis of hypoglycemia is confirmed. The oral glucose tolerance test, often used in the evaluation of such patients, also may give misleading results, because many normal subjects have glucose values below the `normal' range during the test. This may explain why functional hypoglycemia has probably been overdiagnosed during the last several years, giving rise to a description of the syndrome of non-hypoglycemia, in which the patient's symptoms are falsely attributed to hypoglycemia, either by himself or by his physician. Nevertheless, functional hypoglycemia exists and can be improved by proper management.