Bilirubin Production and Hour-Specific Bilirubin Levels

J Perinatol. 2015 Sep;35(9):735-8. doi: 10.1038/jp.2015.32. Epub 2015 Apr 16.


Objective: We assessed the relative contributions of increased bilirubin production (indexed by end-tidal carbon monoxide (CO) concentrations, corrected for ambient CO (ETCOc)) to hour-specific total bilirubin (TB) levels in healthy late preterm and term newborns.

Study design: Post hoc analyses of concurrent ETCOc and TB (at 30±6 h of age) and follow-up TB levels at age 96±12 h and up to 168 h after birth were performed in a cohort of 641 term and late preterm infants.

Results: Increased bilirubin production (hour-specific ETCOc ⩾1.7 p.p.m. at age 30±6 h) was noted in ~80%, 42% and 32% of infants in the high-, intermediate- and low-risk TB zones, respectively. One infant with TB <40th percentile and ETCOc <1.7 p.p.m. developed TB ⩾95th percentile at age 168 h, probably due to decreased bilirubin elimination.

Conclusions: Infants in the high-risk quartile of the hour-specific bilirubin nomogram have a higher mean bilirubin production. Infants with TB levels ⩾95th percentile without increased bilirubin production have impaired bilirubin elimination.

MeSH terms

  • Bilirubin* / biosynthesis
  • Bilirubin* / blood
  • Bilirubin* / metabolism
  • Carbon Monoxide / analysis
  • Female
  • Gestational Age
  • Humans
  • Hyperbilirubinemia* / diagnosis
  • Hyperbilirubinemia* / etiology
  • Infant, Newborn
  • Infant, Premature / blood
  • Male
  • Nomograms
  • Predictive Value of Tests
  • ROC Curve
  • Time Factors


  • Carbon Monoxide
  • Bilirubin