What happens to iron markers immediately after IV iron infusion?

After intravenous iron infusion, serum ferritin rises sharply within 24–48 hours, reflecting the large iron load taken up by macrophages and stored as ferritin. Transferrin saturation (TSAT) may increase modestly or remain normal, since only a fraction of infused iron is immediately released into plasma for binding to transferrin. Over subsequent days to weeks, ferritin gradually declines as stored iron is mobilized to transferrin and used for erythropoiesis.