Asymptomatic hyperammonemia in low birthweight infants

Abstract

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 μM; a value similar.to that reported in adults. Ammonium levels in low birthweight AGA and SGA groups were 47.0 ± 2.0 μM and 45.1 ± 3.3 /tM respectively; significantly elevated (P < 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 < 0.01) decrease in plasma a-ketoglutarate concentration: ± 1.0 μM, in the low birthweight AGA as compared to 20.7 ± 0.6 (μM in the full term AGA infants. There was an inverse linear correlation between plasma concentrations of ammonium and a-ketoglutarate r = —0.86, P < 0.001. Urinary orotate excretion was significantly elevated (P < 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. Speculation: There is a greater accumulation of ammonium in low birthweight as compared to full term infants. This may be a consequence of a developmental delay of one or more of the enzymes required for urea synthesis. Alternatively, the hyperammonemia may be related to arginine and/or ornithine diversion out of the cycle and incomplete repletion of ornithine from glutamate via the Δ′-pyrroline-5-carboxylate pathway. © 1978 International Pediatrics Research Foundation, Inc.