Maintenance of Dose-Dependent Bilirubin Reduction with Ultra-High-Irradiance Phototherapy up to 148 μW/cm2/nm in Severe Neonatal Jaundice

Background/Objectives: Phototherapy is an effective first-line treatment for neonatal jaundice. Previous studies have demonstrated a linear dose-dependent relationship between irradiance and bilirubin reduction during intensive phototherapy up to approximately 55 μW/cm2/nm, although others have suggested that the therapeutic effect plateaus with higher irradiance. However, the efficacy and safety of treatment at these irradiance levels remain unclear. By focusing on newborns with severe jaundice close to the exchange transfusion threshold, we aimed to examine whether the dose-dependent association between phototherapy irradiance and bilirubin reduction is maintained at irradiance levels above 55 μW/cm2/nm. Methods: Here, phototherapy delivered at estimated irradiance levels >55 μW/cm2/nm was defined as ultra-high-irradiance phototherapy. We retrospectively reviewed 92 neonates with severe jaundice admitted to a tertiary neonatal intensive care unit between 2017 and 2024. Severe jaundice was defined as total serum bilirubin levels above or within 2.5 mg/dL of the exchange transfusion threshold. We evaluated the dependence of the bilirubin reduction rate on estimated irradiance and other clinical variables. Results: Only one neonate required exchange transfusion. In multivariable analysis, the bilirubin reduction rate was associated with estimated irradiance (p < 0.001) and total serum bilirubin at phototherapy initiation (p < 0.001). Bilirubin reduction was dose-dependent on estimated irradiance up to 148 μW/cm2/nm (0.31 mg/dL/h per 100 μW/cm2/nm). Transient hyperthermia occurred in 12% of infants. Conclusions: Higher estimated irradiance was associated with greater bilirubin reduction up to 148 μW/cm2/nm. These findings support further prospective evaluation of optimized phototherapy irradiance in severe neonatal jaundice.