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Unbound bilirubin and bilirubin-albumin binding levels of Japanese neonates

Journal of Perinatology volume 45, pages 965–970 (2025)Cite this article

Subjects

Abstract

Objective

To determine postnatal changes in total serum bilirubin (TB), unbound bilirubin (UB), and bilirubin-binding affinity of albumin (Ka) among Japanese newborns.

Study design

In a retrospective study, we evaluated for serum TB, UB, and albumin (Alb) levels, and their calculated UB/TB ratios, and Ka in 786 neonates born ≥36 weeks’ gestation and analyzed to subcategories of three postnatal epochs: first, second, and ≥third weeks.

Result

TB levels were significantly higher (p < 0.01) at age ≥three weeks, while UB levels were significantly higher (p < 0.01) in the first week. UB/TB ratios were significantly lower while calculated Ka values were significantly higher as age-in-weeks increased (p < 0.01).

Conclusion

Hyperbilirubinemia in the first and second weeks of age in neonates born ≥36 weeks’ gestation is associated with higher UB levels or UB/TB ratios with lower Ka and may potentially contribute to the risk of developing bilirubin neurotoxicity with aggravated variations in bilirubin, albumin and Ka.

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Fig. 1: Changes in total serum bilirubin (TB) and unbound bilirubin (UB) levels and UB/TB ratios by postnatal age-in-weeks in neonates ≥36 weeks’ gestation.
Fig. 2: Changes in albumin (Alb) levels and calculated Ka values by postnatal age-in-weeks in neonates ≥ 36 weeks’ gestation.
Fig. 3: Correlation between albumin (Alb) levels or calculated Ka values and unbound bilirubin (UB)/ total serum bilirubin (TB) ratios in neonates ≥36 weeks’ gestation.
Fig. 4: Correlation between unbound bilirubin (UB) levels and total serum bilirubin (TB): albumin molar ratios (BAMRs) in neonates ≥ 36 weeks’ gestation.

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Data availability

The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

The authors sincerely appreciate Dr. Ronald J. Wong (Department of Pediatrics, Stanford University School of Medicine) for his critical review and editing of this manuscript.

Author information

Authors and Affiliations

  1. Department of Neonatology, Takatsuki General Hospital, Takatsuki, Osaka, Japan

    Kazuki Nishizawa & Yoshinori Katayama

  2. Department of Pediatrics, Aijinkai Rehabilitation Hospital, Takatsuki, Osaka, Japan

    Yong-Kye Lee

Authors
  1. Kazuki Nishizawa
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  2. Yoshinori Katayama
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  3. Yong-Kye Lee
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Contributions

KN: Data curation, formal analysis, original draft preparation. YK: Conceptualization, writing-reviewing and editing, Supervision. YL: Conceptualization, reviewing and editing. All authors approved the final manuscript as submitted.

Corresponding author

Correspondence to Yoshinori Katayama.

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Competing interests

The authors declare no competing interests.

Ethics approval

This study was approved by the ethics committee of Takatsuki General Hospital (approval number: 2021–20) and was performed in accordance with the Declaration of Helsinki.

Consent to participate

The ethics committee of Takatsuki General Hospital approved this observational study with a waiver of informed parental consent.

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Nishizawa, K., Katayama, Y. & Lee, YK. Unbound bilirubin and bilirubin-albumin binding levels of Japanese neonates. J Perinatol 45, 965–970 (2025). https://doi.org/10.1038/s41372-025-02266-5

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