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A Novel Method for Measuring Serum Unbound Bilirubin Levels Using Glucose Oxidase–Peroxidase and Bilirubin-Inducible Fluorescent Protein (UnaG): No Influence of Direct Bilirubin

1
Department of Neonatology, Hyogo Prefectural Kobe Children’s Hospital Perinatal Center, Kobe 650-0047, Japan
2
Department of Pediatrics, Kakogawa City Hospital, Kakogawa 675-8511, Japan
3
Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe 657-8501, Japan
4
Department of Developmental Pediatrics, Shizuoka Prefectural Shizuoka Children’s Hospital, Shizuoka 420-8660, Japan
5
Department of Medical Technology, Kobe Tokiwa University, Kobe 653-0838, Japan
6
Department of Pediatrics and Child Health, Nihon University School of Medicine, Tokyo 173-8610, Japan
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Int. J. Mol. Sci. 2020, 21(18), 6778; https://doi.org/10.3390/ijms21186778
Received: 26 August 2020 / Revised: 12 September 2020 / Accepted: 14 September 2020 / Published: 16 September 2020
The glucose oxidase–peroxidase (GOD–POD) method used to measure serum unbound bilirubin (UB) suffers from direct bilirubin (DB) interference. Using a bilirubin-inducible fluorescent protein from eel muscle (UnaG), a novel GOD–POD–UnaG method for measuring UB was developed. Newborn sera with an indirect bilirubin/albumin (iDB/A) molar ratio of <0.5 were classified into four groups of DB/total serum bilirubin (TB) ratios (<5%, 5–10%, 10–20%, and ≥20%), and the correlation between the UB levels and iDB/A ratio was examined. Linear regression analysis was performed to compare UB values from both methods with the iDB/A ratio from 38 sera samples with DB/TB ratio <5% and 11 samples with DB/TB ratio ≥5%. The correlation coefficient (r) between UB values and the iDB/A ratio for the GOD–POD method was 0.8096 (DB/TB ratio <5%, n = 239), 0.7265 (5–10%, n = 29), 0.7165 (10–20%, n = 17), and 0.4816 (≥20%, n = 16). UB values using the GOD–POD–UnaG method highly correlated with the iDB/A ratio in both <5% and ≥5% DB/TB ratio sera (r = 0.887 and 0.806, respectively), whereas a low correlation (r = 0.428) occurred for ≥5% DB/TB ratio sera using the GOD–POD method. Our GOD–POD–UnaG method can measure UB levels regardless of the presence of DB. View Full-Text
Keywords: albumin; analyzer; bilirubin encephalopathy; glucose oxidase-peroxidase method; indirect bilirubin; neonatal intensive care unit albumin; analyzer; bilirubin encephalopathy; glucose oxidase-peroxidase method; indirect bilirubin; neonatal intensive care unit
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Iwatani, S.; Yamana, K.; Nakamura, H.; Nishida, K.; Morisawa, T.; Mizobuchi, M.; Osawa, K.; Iijima, K.; Morioka, I. A Novel Method for Measuring Serum Unbound Bilirubin Levels Using Glucose Oxidase–Peroxidase and Bilirubin-Inducible Fluorescent Protein (UnaG): No Influence of Direct Bilirubin. Int. J. Mol. Sci. 2020, 21, 6778.

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