Background Ferric Carboxymaltose (Ferinject) is a commonly used intravenous iron preparation. Varying degrees of hypophosphataemia have been reported with Ferinject. This is thought to be due to FGF23 mediated renal phosphate wasting, which has been associated with osteomalacia. With only 2 case reports of symptomatic osteomalacia and insufficiency fractures, clinical significance of Ferinject related hypophosphatemia in the overall population receiving it is unclear. Alternative intravenous iron preparation Iron III Isomaltoside (Monofer), has been reported to have a lower incidence of hypophosphatemia compared to Ferinject (Detlie, et. al., 2019) but some case series have reported a higher rate of hypersensitivity reactions (Mulder, et. al., 2018) Aim To investigate the incidence of clinically significant hypophosphataemia in patients receiving Ferinject therapy based at daycase unit at Nottingham University Hospitals. Methods Electronic and paper medical records, including prescription charts, of patients receiving parenteral Ferinject between January 2017 and September 2019 were reviewed. Patients were identified from the local admission database. Data was collected including age, sex, and race, number of Ferinject infusions, Ferinject dose, eGFR, Vitamin D, parathyroid hormone (PTH) and phosphate levels before and after Ferinject infusion. Hospital admissions, symptoms related to hypophosphataemia and need for phosphate replacement was recorded. Normal lab phosphate levels were 0.80-1.50 mmol/ L. Hypophosphatemia was defined as mild (0.65-0.79 mmol/ L), moderate (0.32 to 0.64 mmol/L), and severe (<0.32 mmol/L). Results We identified 400 (251 female and 149 male), patients who had received Ferinject during the study period. 56 (14%) and 51 (13%) patients had phosphate levels tested within 1 year before and after receiving Ferinject respectively. Of these patients, 4 (7%) had hypophosphataemia prior to and, 17 (33%) {3 mild, 13 moderate and 1 severe} after Ferinject therapy. None of the 17 patients had symptoms related to hypophosphataemia. 2 patients with moderate hypophosphataemia incidentally found on routine bloods were admitted for phosphate replacement. 3 patients were admitted for a cause unrelated to hypophosphataemia. Conclusions Our audit demonstrates that in our practice no acute serious adverse events were recorded due to Ferinject related hypophosphatemia. The long term impact of Ferinject-related hypophosphataemia requires larger prospective studies. This is of particular relevance to patients with preexisting risk factors for bone metabolism disorders. It is our practice to correct Vitamin D deficiency where possible prior to administration of Ferinject. It has not been our practice to routinely measure serum phosphate level post infusion.