[Hypophosphatemia in patients with iron-deficiency anemia who received intravenous iron]

When iron-deficiency anemia is treated with intravenous iron, fibroblast growth factor 23 (FGF23) levels may be altered, thereby leading to hypophosphatemia. Our objectives were to determine the timing and incidence of hypophosphatemia following an iron infusion.

A prospective, descriptive, single-center study in adults with iron-deficiency anemia treated with intravenous iron and evaluated at predetermined timepoints.

Twenty-three patients were included; 21 received iron saccharate. The incidence of hypophosphatemia was 73.3%, 52.9%, and 8.3% at 2, 7 and 21 days after the last iron infusion. Significantly lower phosphatemia was observed at 48 h compared to baseline. This difference was not observed at 7 and 21 days. No cases of hypophosphatemia were subsequently reported among patients without hypophosphatemia at their initial visit. Calcemia remained normal in all visits. The cumulative dose of iron did not influence phosphatemia. No significant differences in hemoglobin, parathyroid hormone, FGF23, glomerular filtration rate, and vitamin D were found between patients with or without hypophosphatemia. FGF23 was elevated in 92.3% of patients 7 days after the last iron infusion.

Hypophosphatemia occurred 48 h following the last intravenous iron infusion, regardless of the total dose. No new events were detected in patients who did not present them earlier. Those with normal phosphate levels at 48 h are unlikely to eventually develop hypophosphatemia and therefore do not require further follow-up.