title: Bilirubin production and hour-specific bilirubin levels.
abstract: 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.
  
  
  METHODS
  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.
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: V K
authors.initials: VK
authors.lastname: Bhutani
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Wong
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: H J
authors.initials: HJ
authors.lastname: Vreman
authors.affiliation: Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: D K
authors.initials: DK
authors.lastname: Stevenson
mesh_terms: D001663:Bilirubin / Q000096:biosynthesis / Q000097:blood / Q000378:metabolism; D002248:Carbon Monoxide / Q000032:analysis; D005260:Female; D005865:Gestational Age; D006801:Humans; D006932:Hyperbilirubinemia / Q000175:diagnosis / Q000209:etiology; D007231:Infant, Newborn; D007234:Infant, Premature / Q000097:blood; D008297:Male; D049451:Nomograms; D011237:Predictive Value of Tests; D012372:ROC Curve; D013997:Time Factors
chemical_list: D002248:Carbon Monoxide; D001663:Bilirubin