Supplementary Material for: Transcutaneous versus Total Serum Bilirubin Measurements in Preterm Infants

Introduction: Transcutaneous bilirubin (TcB) measurement offers a noninvasive approach for bilirubin screening; however, its accuracy in preterm infants is unclear. This study determined the agreement between TcB and total serum bilirubin (TSB) among preterm infants. Methods: A multisite prospective cohort study was conducted at 3 NICUs in Ontario, Canada, September 2016 to June 2018. Among 296 preterm infants born at 240/7 to 356/7 weeks, 856 TcB levels were taken at the forehead, sternum, and before and after the initiation of phototherapy with TSB measurements. Bland-Altman plots and 95% limits of agreement (LOA) expressed agreement between TcB and TSB. Results: The overall mean TcB-TSB difference was −24.5 μmol/L (95% LOA −103.3 to 54.3), 1.6 μmol/L (95% LOA −73.4 to 76.5) before phototherapy, and −31.1 μmol/L (95% LOA −105.5 to 43.4) after the initiation of phototherapy. The overall mean TcB-TSB difference was −15.2 μmol/L (95% LOA −86.8 to 56.3) at the forehead and −24.4 μmol/L (95% LOA −112.9 to 64.0) at the sternum. The mean TcB-TSB difference was −31.4 μmol/L (95% LOA −95.3 to 32.4) among infants born 24–28 weeks, −25.5 μmol/L (95% LOA −102.7 to 51.8) at 29–32 weeks, and −15.9 μmol/L (95% LOA −107.4 to 75.6) at 33–35 weeks. Measures did not differ by maternal ethnicity. Conclusion: Among preterm infants, TcB may offer a noninvasive, immediate approach to screening for hyperbilirubinemia with more careful use in preterm infants born at <33 weeks’ gestation, as TcB approaches treatment thresholds. Its underestimation of TSB after the initiation of phototherapy warrants the use of TSB for clinical decision-making after the initiation of phototherapy.