Objective: Neonatal jaundice is the result of an imbalance between bilirubin production and elimination, and our objective was to clarify the contribution of an increase in bilirubin production to hyperbilirubinemia in newborns.
Methods: We measured the end-tidal carbon monoxide concentration corrected for ambient carbon monoxide concentration in 108 jaundiced newborns (total serum bilirubin level >75th percentile) and 164 control newborns in our well-infant nursery, for the first 4 days after birth.
Results: Mean end-tidal carbon monoxide levels decreased in the control infants in the first 4 days but increased in the hyperbilirubinemic group. The differences between the jaundiced and nonjaundiced infants were statistically significant on all days.
Conclusions: Before hospital discharge, most infants with bilirubin levels >75th percentile are producing significantly more bilirubin than those with lower bilirubin levels. Because the ability of newborns to conjugate bilirubin is significantly impaired in the first few days, even a small increase in the rate of production can contribute to the development of hyperbilirubinemia. These data suggest that increased heme catabolism is an important mechanism responsible for hyperbilirubinemia in the first 4 days after birth.