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Open Access Highly Accessed Research article

Cord blood calcium, phosphate, magnesium, and alkaline phosphatase gestational age-specific reference intervals for preterm infants

Tanis R Fenton12*, Andrew W Lyon34 and M Sarah Rose5

Author Affiliations

1 Department of Community Health Sciences, University of Calgary, 3280 Hospital Drive NW, Calgary, Alberta T2N 4Z6, Canada

2 Nutrition Services, Alberta Health Services, 1403 29 Street NW, Calgary, Alberta T2N 2T9, Canada

3 Clinical Biochemistry, Calgary Laboratory Services, 9, 3535 Research Rd. NW, Calgary, Alberta, T2L 2K8, Canada

4 Clinical Biochemistry, Department of Pathology and Laboratory Medicine, University of Calgary, 9, 3535 Research Rd. NW, Calgary, Alberta T2L 2K8, Canada

5 Research Excellence Support Team, Alberta Health Services, Alberta Health, Services, 1403 29 Street NW, Calgary,ABT2N 2T9, Canada

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BMC Pediatrics 2011, 11:76  doi:10.1186/1471-2431-11-76

Published: 31 August 2011



The objective was to determine the influence of gestational age, maternal, and neonatal variables on reference intervals for cord blood bone minerals (calcium, phosphate, magnesium) and related laboratory tests (alkaline phosphatase, and albumin-adjusted calcium), and to develop gestational age specific reference intervals based on infants without influential pathological conditions.


Cross-sectional study. 702 babies were identified as candidates for this study in a regional referral neonatal unit. After exclusions (for anomalies, asphyxia, maternal magnesium sulfate administration, and death), relationships were examined between cord blood serum laboratory analytes (calcium, phosphate, magnesium, alkaline phosphatase, and albumin-adjusted calcium) with gestation age and also with maternal and neonatal variables using multiple linear regression. Infants with influential pathological conditions were omitted from the development of gestational age specific reference intervals for the following categories: 23-27, 28-31, 32-34, 35-36 and > 36 weeks.


Among the 506 preterm and 54 terms infants included in the sample. Phosphate, magnesium, and alkaline phosphatase in cord blood serum decreased with gestational age, calcium increased with gestational age. Those who were triplets, small for gestational age, and those whose mother had pregnancy-induced hypertension were influential for most of the analytes. The reference ranges for the preterm infants ≥ 36 weeks were: phosphate 1.5 to 2.6 mmol/L (4.5 to 8.0 mg/dL), calcium: 2.1 to 3.1 mmol/L (8.3 to 12.4 mg/dL); albumin-adjusted calcium: 2.3 to 3.2 mmol/L (9.1 to 12.9 mg/dL); magnesium 0.6 to 1.0 mmol/L (1.4 to 2.3 mg/dL), and alkaline phosphatase 60 to 301 units/L.


These data suggest that gestational age, as well as potentially pathogenic maternal and neonatal variables should be considered in the development of reference intervals for preterm infants.

Infant; premature; Infant; very low birth weight; reference values; reference ranges