To compare available nomograms in the literature defining trends in bilirubin levels across populations with different risk factor profiles and to study a mathematical bilirubin kinetics model describing the natural course of jaundice and the bilirubin rate of rise needed to cross percentile curves.
We searched PubMed for publications between March 1999 and March 2009 that created transcutaneous nomograms. We performed the same search among abstracts presented in the past 2 years at meetings of the Pediatric Academic Societies or the European Society for Paediatric Research.
Inclusion criteria were gestational age of at least 35 weeks among study subjects, the use of an electronic transcutaneous bilirubinometer, and creation of a nomogram based on hour-specific bilirubin values. Four articles met the selection criteria.
Jaundice risk factors were analyzed, and raw data were analyzed using nonlinear regression to describe trends in bilirubin levels and kinetics. The bilirubin exaggerated rate of rise needed to cross percentile curves was calculated.
Significant differences in bilirubin values exist across populations, and there is substantial variability in rates of rise. Hispanic neonates demonstrate higher rates of rise and later plateaus. Bilirubin rates of rise tend to plateau and become null (equilibrium between bilirubin production and elimination) at about 96 hours of life. Rates of rise needed to cross percentile curves decrease over time but are lower (approximately 0.11 mg/dL/h [to convert bilirubin level to micromoles per liter, multiply by 17.104]) in the first 48 hours of life than previously thought.
Transcutaneous bilirubin levels plateau and then decrease after about 96 hours of life in healthy neonates, with some differences across populations. A bilirubin rate of rise higher than in the previous period implies that bilirubin production exceeds elimination and indicates high risk for subsequent hyperbilirubinemia in neonates.