Leukemoid reaction following ferric carboxymaltose infusion in an elderly patient

Leukemoid reaction, a non-malignant leucocytosis (total leucocyte count≥30 000-50 000 /mm³) is typically triggered by infection, malignancy or drug exposure. Its occurrence after intravenous iron infusion is rare. An elderly man in his mid-70s with a history of prostate cancer (in remission), hypertension and osteoarthritis developed acute onset leucocytosis (>30 000/mm³) with systemic inflammatory signs (myalgia, malaise, elevated C reactive protein), transaminitis and acute kidney injury following his second ferric carboxymaltose infusion for iron deficiency anaemia. Extensive investigation ruled out infection and malignancy. His condition improved with supportive care and returned to baseline, aided by preserved physiological reserve. Though uncommon, leukemoid reaction should be considered as a potential adverse event of ferric carboxymaltose infusion in older adults even when prior doses were tolerated. Incorporating geriatric assessment may help predict resilience and guide management.