Asymptomatic hyperammonemia in low birthweight infants.

At 0-3 days of age the plasma ammonium concentration in full term appropriate for gestational age (AGA) infants was (mean +/- SEM) 27.5 +/- 0.5 micron; a value similar to that reported in adults. Ammonium levels in low birthweight AGA and SGA groups were 47.0 +/- 2.0 micron and 45.1 +/- 3.3 micron respectively; significantly elevated (P less than 0.001) as compared to the full term group. These increased ammonium levels persisted at 3-5 weeks of age. Associated with the hyperammonemia was a significant (P less than 0.01) decrease in plasma alpha-ketoglutarate concentration: 11.8 +/- 1.0 micron, in the low birthweight AGA as compared to 20.7 +/- 0.6 micron in the full term AGA infants. There was an inverse linear correlation between plasma concentrations of ammonium and alpha-ketoglutarate r = -0.86, P less than 0.001. Urinary orotate excretion was significantly elevated (P less than 0.05) in low birthweight AGA infants. There was no difference in the plasma concentrations of glutamine, glutamate, or alanine among the various groups. Hyperammonemia was not associated with neurologic dysfunction.