Iron deficiency and osteoporosis frequently co-exist in hospital patients and often leads to the administration of parenteral bisphosphate therapy alongside intravenous iron. However, case reports have described hypophosphataemia associated with this practice, resulting in patient morbidity, prolonged hospitalisation and readmission. Hypophosphataemia is a recognised complication of ferric carboxymaltose (FCM), driven by increased renal phosphate wasting due to inhibition of fibroblast growth factor 23 (FGF23) cleavage and increased biologically active FGF23 levels. This effect is further exacerbated by antiresorptives through secondary hyperparathyroidism and reduced skeletal phosphate mobilisation. This study aimed to evaluate the incidence and predictors of hypophosphataemia with concurrent intravenous iron and antiresorptive use. This 14-year retrospective cohort study (June 2010 - June 2024) at a single tertiary centre included patients receiving intravenous iron (ferric polymaltose, FCM or ferric sucrose) and denosumab or zoledronic within three months, with serum phosphate measured within 90 days of iron administration. Pharmacy dispensing records were cross-checked with medical and pathology data.  Preliminary data show that among 268 patients (13% male, 87% female; mean age: 83 ± 10 years) receiving concurrent intravenous iron and denosumab, 129 (48.5%) had follow-up results; 46/129 (35.7%) developed hypophosphatemia. Both FCM (n= 19) and ferric polymaltose (n=27) were associated with hypophosphataemia (46% vs 31%, p=0.084). Most cases developed moderate hypophosphataemia (0.32-0.64mmol/L) and 9.5% (n=13) required intravenous phosphate replacement. Affected patients had lower baseline phosphate levels (1.18 ± 0.26 vs 1.08 ± 0.25; p = 0.032) and shorter intervals between denosumab and iron administration (5.5 vs 14 days, p=0.003). Further analysis is underway, with an expected 345 patients in the denosumab group and 164 in the zoledronic acid group with follow-up pathology after iron administration. This will be the largest real-world evaluation of this clinical scenario. Concurrent denosumab and intravenous iron is associated with a high incidence of hypophosphataemia, especially with short treatment intervals. Baseline phosphate levels were within the normal range, limiting predictive value. These findings support avoiding short dosing intervals, routine phosphate monitoring, consideration of lower-risk intravenous iron (eg. ferric derisomaltose), and the need for robust clinical guidelines.