Background: Older patients undergoing hip fracture surgery often have iron deficiency treated with intravenous iron infusions, which can cause hypocalcaemia and hypophosphatemia. They also receive denosumab for osteoporosis, which can cause hypocalcaemia. Currently, it is unclear if combining iron infusions with denosumab increases hypocalcaemia risk further.
Aims: Compare the risk of hypocalcaemia with co-administration of iron infusion and denosumab to iron infusion alone.
Methods: This retrospective cohort study included adults over the age of 60 admitted to the ortho-geriatric units for hip fracture surgery from May 2020 to May 2022. Patients were divided into three groups based on their peri-operative treatment: iron infusion, denosumab or both administered within six weeks. Outcomes, hypocalcaemia (serum calcium <2.15mmol/L) and hypophosphataemia (serum phosphate <0.75mmol/L), were compared among groups in unadjusted and adjusted (age, eGFR, CRP, vitamin D and calcium levels) models.
Results: In this cohort (n=176, mean age±SD:82.8±9, women 77.2%), hypocalcaemia occurred in 8.8% of patients in the iron infusion group (n=66), 13.2% in the denosumab group (n=71), and 29.6% in the combination group (n=30). Compared to the iron infusion group, the odds of hypocalcaemia were significantly higher in the combination group in the unadjusted (OR=4.38, 95%CI:1.27-15.05, p=0.019) and the adjusted models (OR=6.56, 95%CI:1.47-29.24, p=0.014). The odds of hypophosphataemia in the combination group were not different from the iron infusion group (p=0.995). Denosumab demonstrated a protective effect against hypophosphataemia compared to iron infusion (p=0.044).
Conclusion: Co-administration of iron infusion and denosumab increases the risk of hypocalcaemia. We suggest pre-emptive monitoring to avoid hypocalcaemia-related complications.