Alterations in Serum Magnesium Levels in Hyperbilirubinemic Neonates Before and After Phototherapy

Background: Bilirubin binds to cell membrane phospholipids, including N-methyl D-aspartate receptor, and causes excessive activation that can lead to neurotoxic effects. Since magnesium is an important inhibitor of this receptor, a comparison can be made between the physiological effects of magnesium and the neurological effects of bilirubin. This study aimed to compare changes in serum magnesium levels before and after phototherapy in hyperbilirubinemic newborns. Methods: This retrospective cross-sectional study examined full-term newborns with hyperbilirubinemia. These newborns were admitted between 2012 and 2014 to the Neonatal Unit of Children's Medical Center in Tehran, Iran. Based on the amount of bilirubin upon admission, participants were divided into three groups of mild (<18 mg/dl), moderate (18-20 mg/dl), and high (>20 mg/dl). The total serum magnesium levels were measured before and 12-24 h after phototherapy. Results: A total of 143 newborns were included in this study. A significant difference was observed between serum magnesium levels before (2.42 +/- 0.46 mg/dl) and after (2.07 +/- 0.32 mg/dl) phototherapy (P<0.001). This difference was observed in all etiologies of icterus. Conclusion: The magnesium level decreased significantly after the completion of jaundice treatment for all causes of the condition. These findings raise the hypothesis that an increase in the level of extracellular magnesium is a defense mechanism that reduces the neurotoxic effects of bilirubin.