Differential diagnosis of hypoglycemia in children by responses to fasting and 2-deoxyglucose

Abstract

The potential usefulness of the fasting test and the 2-deoxyglucose (2DG) test for differential diagnosis of childhood hypoglycemia was evaluated by comparing responses to these tests in control children and in 28 children with confirmed hypoglycemia from either known or undifferentiated causes. Twelve hypoglycemic subjects with independently established endocrine or metabolic disorders became definitely hypoglycemic within 24 hours of fasting. The diagnosis of hyperinsulinism was confirmed in four by the consistent finding of elevated fasting plasma insulin levels (greater than 4 μU/mL with glucose less than 40 mg/dL); the fasting levels of plasma β-hydroxybutyrate (BOHB) and free fatty acids (FFA) were low relative to glucose, but these abnormalities were variable and not specific to hyperinsulinism. In a single subject with idiopathic adrenal cortical insufficiency cortisol remained unusually low (less than 2 μg/dL) in both tests. Neither test distinguished two children with growth hormone deficiency. In two children with defective gluconeogenesis (glucose-6-phosphatase deficiency), the fasting plasma alanine level was distinctively high relative to glucose. A patient with defective ketogenesis due to carnitine deficiency had an abnormally low plasma BOHB level associated with a high FFA level. Among the 16 subjects with undifferentiated hypoglycemia, only nine became hypoglycemic within 24 hours of fasting; three remained within the control range even after 36 hours. After receiving 2DG (50 mg/kg), 11 of these children responded subnormally with an increase of plasma glucose less than 15 mg/dL, including all of the subjects who failed to become hypoglycemic within 24 hours of fasting. One subject with an undifferentiated cause had a definitely elevated insulin level during fasting hypoglycemia. Epinephrine deficiency was the most common finding among the subjects with undifferentiated causes (five cases). This was established by subnormal urine epinephrine responses to both fasting hypoglycemia and 2DG stimulation (less than 80 ng/mg creatinine) and by a lack of an increase in the levels of plasma glucose, FFA, BOHB, and lactate after 2DG. Three other subjects had diminished epinephrine and metabolic responses to 2DG but the epinephrine responses to fasting and 2DG were inconsistent. No subjects were identified with glucagon deficiency. Plasma alanine and glucose levels were proportionately decreased in all of the undifferentiated subjects. An abnormally low alanine level was not characteristic of any particular subgroup. None of the hypoglycemic children were abnormally ketotic, in that the plasma BOHB level was not unusually high relative to glucose. After these tests seven of the 16 children remained undifferentiated with no specific endocrine or metabolic abnormality identified. It is concluded that fasting is the most useful test for confirming diagnoses of hyperinsulinism and inherited disorders of gluconeogenesis or ketogenesis. The 2DG test is valuable for the detection of epinephrine unresponsiveness, which is the most common abnormality found among children with undifferentiated hypoglycemia. The combined use of these tests makes it unnecessary to extend fasting for more than 24 hours.