A retrospective analysis of the prevalence of hypophosphatemia and hypocalcemia after intravenous iron polymaltose in the inpatient setting

Hypophosphatemia occurring after ferric carboxymaltose or iron polymaltose infusion is common and has been well-characterized. Post-iron infusion hypocalcemia has been documented in case reports, but there is no data on the prevalence of hypocalcemia developing after i.v. iron infusion. In this retrospective cohort study, we sought to characterize integrated daily changes in serum phosphate and corrected calcium levels before and after iron infusion in a real-world inpatient setting. Inpatients who received i.v. iron polymaltose at the Royal Brisbane and Women's Hospital (Queensland, Australia) between January 2020 and September 2021 were included. We extracted all results for serum phosphate and corrected calcium levels for 21 d before and after iron infusion. A total of 741 patients with 8272 blood samples were included. The serum phosphate concentration reduced by an average of 30.6% (95% CI 28.2-32.9) in the 5 d following infusion. Serum phosphate reached a nadir at day 5 before incrementing, but still remained below baseline by the end of the study period. Conversely, serum corrected calcium levels increased within 1 d of iron polymaltose infusion and then dropped over the following 5 d. There was a significant increase in the prevalence of hypophosphatemia developing after iron polymaltose infusion (34% post-infusion vs 8% pre-infusion, <i>p</i>-value < .001). Hypophosphatemia occurred most commonly within the first week after iron infusion, whereas hypocalcemia was more frequently a later occurrence. Our results have enhanced the understanding of the day-to-day biochemical changes occurring after iron infusion as well as the prevalence and timing of post-iron infusion hypophosphatemia and hypocalcemia.