Related Experiment Video
Updated: Mar 7, 2026

Transcutaneous Microcirculatory Imaging in Preterm Neonates
Published on: December 31, 2015
Unconjugated free bilirubin in preterm infants
Lori W E van der Schoor1, Peter H Dijk2, Henkjan J Verkade1
1Division of Pediatric Gastroenterology and Hepatology, Department of Pediatrics, Beatrix Children's Hospital, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
Background:
Hyperbilirubinemia guidelines are based on total serum bilirubin (TSB), in combination with either gestational age (GA) or birth weight (BW), postnatal age and specific risk factors. However, TSB is a poor predictor of bilirubin-induced neurotoxicity (BIND). Free unconjugated bilirubin (UCBfree) and the UCBfree/TSB ratio are more directly related to BIND, but data on their postnatal courses are unknown.
Aims:
To characterize the postnatal courses of UCBfree and UCBfree/TSB ratio, and assess their relationships with clinical characteristics.
Subjects:
72 preterm infants≤32weeks GA, admitted to the University Medical Center Groningen, The Netherlands.
Study Design:
During the first postnatal week, bilirubin plasma parameters were analyzed and their relationship with clinical parameters was analyzed. Postnatal changes were analyzed using Generalized Estimating Equations. Data are expressed as medians [ranges].
Results:
Less than 10% of the cohort (GA: 29 [26-31] weeks; BW: 1165 [600-1975] g) showed hyperbilirubinemic risk factors. We observed a large variation in UCBfree (27 [1-197] nmol/L), that could partly be explained by postnatal age and gender, but not by other risk factors. Maximal UCBfree levels of 50 [13-197] nmol/L occurred at day 4 and were higher in males. In contrast to TSB, UCBfree/TSB ratios (0.19 [0.01-1.04]) were higher in infants with low GA/BW.
Conclusion:
UCBfree levels vary considerably in preterm infants, despite a low incidence of hyperbilirubinemic risk factors and similar TSB-based phototherapy treatment. UCBfree could not be predicted by GA or BW, but UCBfree/TSB ratios are highest in the smallest preterms, while they have the lowest TSB levels.
Related Concept Videos
Transcytosis of IgG
IgG molecules from a mother undergo transcytosis starting around 13 weeks of gestation. The amount of IgG transferred and entering the fetal blood circulation increases with...
Drug Distribution: Plasma Protein Binding
Pharmacokinetics in Pediatric Patients: Drug Metabolism
Development of Immunocompetence
The initial cells that migrate from the fetal thymus settle within the skin and epithelial tissues lining the mouth, digestive tract, and in females, the uterus and vagina. These cells, including skin-based dendritic cells, serve as antigen-presenting cells, playing a key role in T cell activation.
Subsequent T...
Inborn Errors of Metabolism
Lifecycle of Erythrocytes
The resident phagocytic macrophages deal with these damaged cells by engulfing them and separating their globin and heme groups....

