When would you consider intravenous (IV) iron infusion for patients with iron deficiency anemia?

When to Consider IV Iron Infusion

Intravenous iron should be considered as first-line treatment when hemoglobin is below 10 g/dL, when oral iron is not tolerated or ineffective, in patients with active inflammatory conditions (especially inflammatory bowel disease), when rapid correction is needed, or in malabsorptive states. 1

Primary Indications for IV Iron

Hemoglobin-Based Criteria

• Severe anemia (Hb <10 g/dL): IV iron is preferred over oral supplementation due to faster response and better efficacy 1
• Moderate anemia (Hb 10-12 g/dL in women, 10-13 g/dL in men): Consider IV iron if oral therapy fails or is contraindicated 1

Oral Iron Failure or Intolerance

• Intolerance to oral iron: Gastrointestinal side effects (nausea, constipation, metallic taste) occur frequently and justify switching to IV therapy 1
• Inadequate response to oral iron: If hemoglobin fails to increase by at least 1 g/dL within 2 weeks, or ferritin doesn't rise within 1 month of adherent oral therapy, switch to IV iron 1
• Oral iron should be given once daily at most, as hepcidin elevation blocks further absorption for up to 48 hours 1

Disease-Specific Indications

Inflammatory Bowel Disease (IBD)

• Active IBD: IV iron is first-line therapy due to impaired absorption and potential disease exacerbation from oral iron (via reactive oxygen species generation) 1
• Functional iron deficiency: When ferritin is 100-300 ng/mL with transferrin saturation <20%, IV iron is preferred 1

Post-Bariatric Surgery

• IV iron is indicated when iron deficiency anemia develops, as duodenal absorption is disrupted 1

Chronic Kidney Disease

• Consider IV iron for functional iron deficiency (ferritin <800 ng/mL and transferrin saturation <20%) 1
• IV iron is superior to oral iron in this population 1

Heart Failure

• IV iron improves exercise capacity in patients with heart failure (NYHA class II/III) and iron deficiency (ferritin <100 ng/mL or 100-300 ng/mL with TSAT <20%) 2

Cancer-Related Anemia

• IV iron combined with erythropoiesis-stimulating agents (ESAs) is more effective than ESA alone 1
• Consider when ferritin <800 ng/mL and transferrin saturation <20% in patients receiving chemotherapy 1

Clinical Situations Requiring Rapid Correction

• Hemodynamic instability with acute anemia: IV iron may be considered alongside transfusion protocols 1
• Severe anemia-related fatigue: When quality of life is significantly impaired 1
• Preoperative optimization: When surgery is planned and time is limited 1

Dosing Considerations

Total Iron Deficit

• The average iron deficit in iron deficiency anemia patients is approximately 1,400-1,500 mg 3
• For patients ≥50 kg: Administer 1,500 mg total (750 mg × 2 doses separated by ≥7 days) 1, 2
• For patients <50 kg: Administer 15 mg/kg × 2 doses separated by ≥7 days 1, 2
• A 1,000 mg cumulative dose may be insufficient for most patients and leads to higher retreatment rates 3

Formulation Selection

• Prefer high-dose formulations that allow 1-2 infusions to complete therapy (ferric carboxymaltose, ferric derisomaltose, low-molecular-weight iron dextran) over those requiring multiple visits 1
• All modern IV iron formulations have comparable safety profiles with <1% risk of moderate-to-severe reactions 4, 5

Safety Monitoring

Common Pitfalls to Avoid

• Hypophosphatemia: Check serum phosphate in patients requiring repeat courses within 3 months, especially with ferric carboxymaltose (affects 50-74% of patients) 2, 4
• Avoid test doses: Not required for modern formulations except iron dextran 1
• Avoid intramuscular iron: Painful, tissue-damaging, and no more effective than oral or IV routes 1

Infusion Reactions

• Most reactions are complement activation-related pseudo-allergy (CARPA), not true anaphylaxis 1
• For mild reactions: Stop infusion, restart after 15 minutes at slower rate 1
• Avoid diphenhydramine: Side effects can mimic worsening reactions 1
• True anaphylaxis is extremely rare (approximately 1:200,000) 1

Expected Response

• Hemoglobin should increase by ≥2 g/dL within 4 weeks of IV iron therapy 1
• Faster response compared to oral iron (mean increase of 2.9 g/dL vs 2.2 g/dL in comparative studies) 6
• Ferritin typically increases significantly within 2 weeks of IV administration 2

When Oral Iron May Still Be Appropriate

• Mild anemia (Hb >10 g/dL) without active inflammation or malabsorption 1
• Patients who tolerate oral iron and have time for gradual correction 1
• No contraindications to oral absorption 1