Objectives:Gamma-glutamyl transferase (GGT) is commonly measured in newborn infants as a sensitive liver function test; however, reference ranges are mostly based on early studies, including relatively small number of patients. The aim of this study was to emphasise recently changed GGT values because of changed newborns profile admitted to neonatal intensive care units (NICUs) and establish new cross-sectional reference ranges for the serum GGT levels in a cohort of neonates between 26 and 42 weeks' gestational age in 1 centre.Methods:From January 1, 2010 to December 31, 2012, liver function tests including serum GGT measurements were performed in 705 newborns who were admitted to NICUs because of different aetiologies at Gazi University School of Medicine Hospital, Ankara, Turkey. Infants with Apgar score <8 at the fifth minute, any metabolic or liver disease, cholestasis, congenital infection, culture-proven sepsis, elevated serum aminotransferases, and who were treated with phenobarbital were excluded. Clinical and laboratory data of 583 neonates were analysed retrospectively. GGT was measured by enzymatic method using the Abbott Architect C16000 autoanalyser. Mean, 2.5th, and 97.5th percentiles were used to express the reference range data.Results:Four hundred sixty-one GGT values of 200 preterm infants and 501 GGT values of 383 term infants during the first 28 days after birth were analysed. Serum GGT levels of preterm infants in the first 7 days and between 8 and 28 days after delivery were (meanstandard deviation; 141.81 +/- 88.56 U/L and 131.17 +/- 85.53 U/L) similar to term infants (139.90 +/- 86.46 U/L and 144.56 +/- 86.51 U/L), respectively (P=0.649 and P=0.087). Serum GGT levels were found to be significantly higher in male infants (no need of query) (145.98 +/- 93.68 U/L) than female infants (132.18 +/- 78.97 U/L) (P=0.035), and infants born vaginally (152.24 +/- 90.71 U/L) also had higher serum GGT activity than those born by caesarean section (135.38 +/- 85.37 U/L) (P=0.005).Conclusions:A new reference range for serum GGT levels that is higher than previous reference values can identify neonates with truly abnormal results and prevent unnecessary interventions.