IV iron is used when oral iron is ineffective, not tolerated, or too slow to correct deficiency.
Typical situations include:
- Malabsorption (e.g., celiac disease, inflammatory bowel disease, bariatric surgery)
- Ongoing blood loss exceeding oral absorption (e.g., heavy menstrual bleeding, GI bleeding)
- Inflammatory states or CKD, where hepcidin blocks intestinal iron uptake
- Intolerance to oral iron (nausea, constipation, poor adherence)
- Need for rapid repletion, such as preoperative anemia, late pregnancy, or severe deficiency with symptoms
In short, IV iron is chosen when speed, absorption, or tolerance make oral therapy impractical.