Background: Neonatal hyperbilirubinemia remains of concern because of the potential danger for the central nervous system. Because urobilinogen is a nontoxic derivative of bilirubin, the current study was conducted to examine the fecal excretion of urobilinoids and bilirubin in healthy newborns and infants, as well as their intestinal bacteria capable of reducing bilirubin, to assess a possible relation to serum bilirubin levels during the first weeks of life.
Methods: Bilirubin pigments, urobilinoids, and porphyrins were measured in stools of infants during the first week (group A, n = 60) and between the second week and the first 6 months of life (group B, n = 64). Microbiologic analysis of stools was performed in selected cases and bilirubin-converting activity of isolated bacteria was determined in vitro.
Results: Urobilinoids were detectable in stools of 57% of the neonates at day 5, but not before. However, fecal urobilinoid production on that day was only a fraction of that observed in adults (0.07 vs. 0.7-3.6 mg/kg per day), whereas at week 6 it increased significantly to an average of 0.9 mg/kg per day. Microbiologic analysis of neonatal stools revealed two novel bacterial strains of Clostridium perfringens and Clostridium difficile capable of reducing bilirubin to urobilinoids.
Conclusions: Urobilinoids can be detected in stools of 57% of newborns at day 5 after delivery. However, the urobilinoid production during the first week of life is quantitatively insufficient to contribute significantly to the removal of bilirubin. Enhancement of the microbial conversion of bilirubin could decrease the intestinal concentration of bilirubin and may decrease the degree or enhance the removal of neonatal hyperbilirubinemia.