An Audit of Hypophosphatemia after Intravenous Iron Therapy

Background Due to the gastrointestinal side-effects of oral iron supplementation in patients with iron deficiency anaemia, which impairs tolerance - many acute medical and haematology day units provide intravenous iron replacement therapy as day cases. Hypophosphatemia is a frequent side effect following intravenous iron administration, which can persist for weeks or months, is under-recognised in clinical practice and can lead to patients presenting with typical features to the emergency departments. Aim We designed an audit to measure the incidence of symptomatic hypophosphatemia after intravenous iron therapy to develop monitoring, prevention, and treatment strategy in a secondary care hospital setting. Methods We audited a convenience sample of consecutive patients who attended an acute day-care assessment unit for intravenous (IV) iron infusion (ferric carboxymaltose). All patients had serum phosphate levels checked after IV iron infusion at different intervals, from 1- 6 weeks. The cohort was divided into two groups based on the occurrence of hypophosphataemia - early (1-3 weeks) and late (>3-6 weeks). Results We included 35 patients referred from primary care, gastroenterology, gynaecology, and acute internal medicine. 19 (55%) developed hypophosphatemia after receiving a single IV iron infusion and almost 100% after more than one dose. Hypophosphatemia in some patients lasted up to 12 weeks. Conclusion Hypophosphatemia was frequent after a single dose and almost universal after multiple doses of IV Iron, which can persist for many weeks. Clinicians prescribing ferric carboxymaltose (Ferinject®) should be aware of hypophosphataemia, which could be mild, moderate, or severe and can last for months.