Percentile-based reference values for serum alkaline phosphatase at birth in Japanese preterm and term infants: A retrospective cohort study

Alkaline phosphatase (ALP) is a key marker for assessing bone metabolism in neonates. The reference values at birth have not been established for Japanese neonates. This study aimed to determine the clinical factors affecting ALP levels and establish percentile-based reference values for preterm and term infants at birth. A total of 663 Japanese neonates were analyzed using data collected within 24 hours of birth. Univariate and multivariate analyses identified clinical factors affecting ALP levels, and percentile values (10th, 25th, 50th, 75th, and 90th percentiles) were calculated for preterm and term infants. Serum ALP isoenzymes were measured in infants, and the percentage of isoenzymes was evaluated. Univariate and multivariate analyses revealed that maternal magnesium sulfate administration and gestational age at birth were significant factors affecting ALP levels. Preterm infants had significantly higher ALP values compared with term infants (P < 0001, the 50th percentile values were 224 and 185 U/L, respectively); therefore, we developed reference values for preterm and term infants, separately. The 10th, 25th, 50th, 75th, and 90th percentile values of ALP at birth were 148, 179, 224, 267, and 338 U/L for preterm infants, and 129, 152, 185, 233, and 286 U/L for term infants, respectively. Bone-specific ALP3 isozyme accounted for 81.3% of the total ALP at birth. This is the first study to establish ALP reference values for Japanese neonates. Maternal magnesium sulfate use and gestational age were identified as key factors affecting ALP levels in Japanese neonates.