Guidelines for Iron Supplementation: Oral vs. Intravenous
Oral iron should be first-line treatment for most patients with iron deficiency anemia who have mild anemia, clinically inactive disease, and no prior intolerance to oral iron, while intravenous iron is preferred for patients with active inflammatory disease, hemoglobin below 10 g/dL, prior oral iron intolerance, or malabsorption. 1, 2
When to Use Oral Iron
Oral iron is appropriate for:
- Patients with mild anemia (hemoglobin >10 g/dL) and clinically inactive disease 1
- Premenopausal women without severe anemia 1
- Patients who have not previously been intolerant to oral iron 1
- Asymptomatic patients without malabsorption syndromes 1
Dosing recommendations for oral iron:
- Standard dose: 100-200 mg elemental iron daily 1, 3
- Lower doses (60-100 mg daily) or alternate-day dosing may improve tolerability while maintaining efficacy 1, 4
- Response should be evident within 4 weeks, with hemoglobin increase of at least 1.0 g/dL 2, 5
- Continue treatment for 3-6 months to replenish iron stores 3
Key pitfall: If hemoglobin fails to increase by at least 1.0 g/dL at day 14, this predicts poor overall response to oral iron (sensitivity 90.1%, specificity 79.3%), and transition to IV iron should be considered. 5
When to Use Intravenous Iron
IV iron should be considered first-line treatment in:
- Patients with clinically active inflammatory bowel disease 1, 2
- Hemoglobin below 10 g/dL (100 g/L) 1, 2
- Previous intolerance to oral iron 1, 2
- Patients requiring erythropoiesis-stimulating agents 1
- Malabsorption syndromes (celiac disease, prior gastric surgery, chronic inflammation) 1, 3
- Chronic kidney disease or heart failure 1, 4
- When blood loss exceeds the ability to replete iron orally 1
The European Crohn's and Colitis Organization concluded that "IV iron is more effective, shows a faster response, and is better tolerated than oral iron" in inflammatory conditions. 1
Dosing for Intravenous Iron
For iron deficiency anemia:
- Patients ≥50 kg: 750 mg IV in two doses separated by at least 7 days (total 1,500 mg per course) 6
- Patients <50 kg: 15 mg/kg body weight IV in two doses separated by at least 7 days 6
- Alternative single-dose option: 15 mg/kg up to maximum 1,000 mg IV as single dose 6
- Dosing is typically based on baseline hemoglobin and body weight 1
For iron deficiency in heart failure (NYHA class II/III):
- Complex weight and hemoglobin-based algorithm with maintenance dosing at 12,24, and 36 weeks 6
Monitoring and Follow-up
Laboratory screening should include:
- Complete blood count, serum ferritin, and C-reactive protein 1, 2
- In patients without inflammation: serum ferritin <30 μg/L indicates iron deficiency 1, 2
- In patients with inflammation: serum ferritin up to 100 μg/L may still indicate iron deficiency 1, 2
Monitoring frequency:
- Patients in remission or mild disease: every 6-12 months 1, 2
- Patients with active disease: every 3 months 1, 2
- After IV iron treatment: re-treat when ferritin drops below 100 μg/L or hemoglobin below 12-13 g/dL (gender-dependent) 1
Important Safety Considerations
For IV iron:
- Check serum phosphate levels in patients requiring repeat courses, especially if within 3 months, due to risk of hypophosphatemia 6, 7
- Monitor for allergic reactions, though serious adverse events are rare 1
- Avoid extravasation as brown discoloration may be long-lasting 6
- Never use intramuscular iron due to pain, tissue damage, and unacceptable side effects 8
For oral iron:
- Gastrointestinal intolerance is common 1
- Taking with food improves tolerability but decreases absorption 1
- Alternate-day dosing may improve tolerability without significantly compromising efficacy 1, 4
- In inflammatory bowel disease, oral iron may exacerbate inflammation even in mild anemia 2
Treatment Goals
The goal of iron supplementation is to normalize hemoglobin levels AND replenish iron stores, not just correct anemia. 1, 2 An acceptable response is hemoglobin increase of at least 2 g/dL within 4 weeks of treatment. 2, 5