Case Report: Usefulness of transcutaneous bilirubin measurement for the early detection of severe hyperbilirubinemia due to late-onset hemolysis in an extremely low birth weight infant.

BACKGROUND: Late-onset hemolysis is a rare but potentially severe complication in extremely preterm infants and may cause rapid increases in bilirubin levels requiring intensive treatment, including exchange transfusion. Phototherapy for neonatal jaundice is guided by total serum bilirubin (TSB) and unbound bilirubin (UB) levels; however, in extremely low-birth-weight infants (ELBWIs), defined as neonates with a birth weight of less than 1,000 g, bilirubin neurotoxicity may occur at lower thresholds, and severe hyperbilirubinemia can develop unexpectedly beyond the acute neonatal phase. Therefore, early recognition of progressive hyperbilirubinemia is essential in this high-risk population. CASE PRESENTATION: We report the case of a male extremely low-birth-weight infant born at 23 weeks and 1 day of gestation with a birth weight of 598 g who developed severe hyperbilirubinemia due to late-onset hemolysis on day of life (DOL) 15. Serial transcutaneous bilirubin (TcB) measurements revealed a rapid increase in bilirubin levels from 5.5 mg/dL to 14.3 mg/dL between DOL 14 and 15, prompting further evaluation. At DOL 15, total serum bilirubin (TSB) and unbound bilirubin (UB) levels were 18.0 mg/dL and 2.00 μg/dL, respectively, exceeding the exchange transfusion threshold. High-intensity phototherapy, albumin administration, and subsequent exchange transfusion were performed. Laboratory findings, including elevated carboxyhemoglobin and methemoglobin levels, supported the diagnosis of late-onset hemolytic jaundice. The infant recovered without recurrence of jaundice or neurological abnormalities during follow-up. CONCLUSION: Late-onset hemolysis can occur even in extremely immature infants and may lead to severe hyperbilirubinemia requiring exchange transfusion. Systematic bilirubin surveillance, including non-invasive monitoring approaches such as TcB, may help reduce diagnostic delays and mitigate the risk of bilirubin neurotoxicity in high-risk preterm infants. In this case, serial TcB measurements contributed to the early detection of rapidly increasing bilirubin levels and facilitated timely intervention.