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Association between the calcium-to-phosphorus ratio and early hypophosphatemia in preterm infants receiving parenteral nutrition in Korea: a retrospective cohort study
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Miseon Han, Jin Ok Kyun, Yoong-A Suh, Jang Hoon Lee
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Received November 11, 2025 Accepted January 26, 2026 Published online March 17, 2026
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DOI: https://doi.org/10.15747/ACNM.25.0039
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 Abstract
- Purpose
This study aimed to evaluate the association between the calcium-to-phosphorus (Ca/P) ratio and serum phosphate levels in preterm infants receiving total parenteral nutrition (TPN) and to explore Ca/P ratio ranges associated with hypophosphatemia.
Methods
We retrospectively reviewed the medical records of preterm infants admitted to the neonatal intensive care unit at Ajou University Hospital between January 2022 and June 2024. The review focused on TPN composition and serum electrolyte changes during the first week of life. Based on the cumulative Ca/P ratio during this period, infants were categorized into two groups: Ca/P-Low (mass ratio ≤1.3) and Ca/P-High (mass ratio >1.3).
Results
A total of 117 preterm infants were included in the analysis (Ca/P-Low group, n=46; Ca/P-High group, n=71). During the first week of life, the cumulative phosphorus deficit was significantly greater in the Ca/P-High group (61.4 mg/kg vs. 8.5 mg/kg; P<0.001). By day of life (DOL) 7, both hypophosphatemia and severe hypophosphatemia had increased markedly in the Ca/P-High group compared with DOL 3. In the Ca/P-High group, the incidence of hypophosphatemia increased from 44.4% on DOL 3 to 75.0% on DOL 7, while the incidence of severe hypophosphatemia increased from 4.8% to 23.1%.
Conclusion
The Ca/P ratio was associated with hypophosphatemia in preterm infants receiving parenteral nutrition. These findings suggest that parenteral nutrition strategies may require phase-adapted Ca/P ratios rather than a fixed ratio during the first week of life. A higher ratio may be appropriate during DOL 0–2, when amino acid intake is low, whereas a lower ratio may be preferable during DOL 3–6, particularly when overall calcium and phosphorus supply is suboptimal.
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