The diagnosis of insulinoma in a child in the absence of fasting hyperinsulinemia.

This report concerns an 8-year-old girl with fasting hypoglycemia caused by a functional islet cell adenoma. During two separate fasting studies the blood glucose concentrations decreased to abnormally low levels yet the serum concentrations of insulin were consistently within the accepted range of normal. This report illustrates the diagnostic value of three simple functional tests--the inhibitory effect of insulin on ketogenesis and on glycogenolysis and the stimulatory effect of leucine on insulin secretion.