Comparative absorption of [13C]glucose and [13C]lactose by premature infants.

Oxidation of orally administered [13C]glucose and [13C]lactose and fecal recovery of malabsorbed substrates were determined in two groups of premature infants. Eighteen studies were performed with six infants at Johns Hopkins Hospital (JHH); 24 studies were performed with nine infants at Columbus Children's Hospital (CCH). The two groups differed in that JHH infants had shorter gestations but were older when studied. Fecal 13C loss after [13C]glucose administration did not differ between the two groups. Compared with glucose, the metabolism of lactose appeared to involve more malabsorption and colonic fermentation in JHH infants than in CCH infants and resulted in higher fecal losses of substrate carbon. Maturation appeared to involve increased proximal intestinal absorption and greater retention of absorbed carbohydrate. Simultaneous absorption of substrate from the small and large intestine may limit the usefulness of breath tests for 13C in the premature infant.