Unconjugated free bilirubin in preterm infants.
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.



To characterize the postnatal courses of UCBfree and UCBfree/TSB ratio, and assess their relationships with clinical characteristics.



72 preterm infants≤32weeks GA, admitted to the University Medical Center Groningen, The Netherlands.



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].



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.



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.
Division 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. Electronic address: l.w.e.van.der.schoor@umcg.nl.
Lori W E
LW
van der Schoor
Division of Neonatology, Department of Pediatrics, Beatrix Children's Hospital, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
Peter H
PH
Dijk
Division 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.
Henkjan J
HJ
Verkade
Division of Neonatology, Department of Pediatrics, Beatrix Children's Hospital, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
Anna C J
AC
Kamsma
Division of Neonatology, Department of Pediatrics, Beatrix Children's Hospital, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
Andrea B
AB
Schreuder
Department of Epidemiology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
Henk
H
Groen
Division of Neonatology, Department of Pediatrics, Beatrix Children's Hospital, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
Christian V
CV
Hulzebos
D001663:Bilirubin / Q000097:blood*; D001724:Birth Weight; D005260:Female; D005865:Gestational Age; D006801:Humans; D006932:Hyperbilirubinemia / Q000097:blood* / Q000453:epidemiology; D007231:Infant, Newborn; D007234:Infant, Premature / Q000097:blood*; D008297:Male
D001663:Bilirubin
Free bilirubin; Preterm infants; Unconjugated hyperbilirubinemia