New percentiles of gamma-glutamyl transferase serum levels in infants and the role of breastfeeding

Background: Normal gamma-glutamyl transferase (GGT) values in infant serum remain poorly defined. Establishing accurate reference ranges during infancy is essential for diagnosing hepatobiliary disorders such as biliary atresia and progressive familial intrahepatic cholestasis. To establish reference percentiles for GGT, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) in infants, and assess influence of breastfeeding. Methods: A retrospective, single-center, longitudinal study including 469 healthy infants was conducted. Liver function was tested from birth to 18 months, and the effects of breastfeeding were analyzed. Results: GGT levels were higher in the first months of life and progressively declined over time. Breastfeeding in the first month of life was associated with higher levels of GGT, total bilirubin (TB), and AST compared to infants who were mixed-fed or exclusively formula-fed. Specifically, breastfed infants had a median GGT of 79 IU/L, while mixed-fed and formula-fed infants had GGT levels of 61 IU/L and 46.5 IU/L, respectively. Similarly, TB was 3.3 mg/dL in breastfed infants, 1.7 mg/dL in mixed-fed, and 1.1 mg/dL in formula-fed. Median AST levels were also highest in breastfed infants (36 IU/L), followed by mixed-fed (33.5 IU/L) and formula-fed (31 IU/L). A positive correlation was observed between GGT and TB (P < 0.001). Conclusions: Age- and sex-specific reference percentiles are provided for GGT, AST, and ALT in infants younger than 18 months. GGT, TB, and AST are physiologically elevated, particularly among breastfed infants.