Bilirubin Photoisomers in Neonatal Jaundice

Phototherapy is the standard treatment for neonatal hyperbilirubinemia. During phototherapy, the highly lipophilic bilirubin is converted into more hydrophilic photoisomers, which can be more easily excreted from the body. This process typically lowers bilirubin levels to non-harmful concentrations. However, despite decades of research into the formation and role of bilirubin photoisomers, methodological limitations and the compound's complex biochemistry have hindered comprehensive understanding. This review provides an updated overview of current knowledge on bilirubin photoisomers, including their basic chemistry, analytical quantification, clinical relevance, and future research directions. Improved insight into the mechanism of photoisomer formation and kinetics may inform optimization of phototherapy parameters, including light intensity and wavelength, and offer additional indicators of treatment efficacy beyond total bilirubin concentration. Advances in sensitive and standardized mass spectrometry techniques now enable more accurate measurement of different bilirubin isomers and serve as a first step towards a deeper insight into the clinical relevance of photoisomers.