What ferritin level indicates the need for iron infusion?

Ferritin Level for Iron Infusion

Intravenous iron should be initiated when serum ferritin is < 100 ng/mL combined with transferrin saturation < 20%, or when ferritin is < 30 ng/mL regardless of transferrin saturation. 1

Diagnostic Thresholds for IV Iron

In Patients Without Inflammation

• Ferritin < 30 ng/mL confirms absolute iron deficiency and warrants IV iron consideration, particularly when oral iron has failed or is contraindicated. 1, 2
• Transferrin saturation < 16–20% signals iron deficiency requiring treatment. 1, 2

In Patients With Inflammation or Chronic Disease

• Ferritin < 100 ng/mL AND transferrin saturation < 20% indicates iron deficiency requiring supplementation, because inflammation elevates ferritin independently of true iron stores. 1, 3, 2
• Ferritin values between 30–100 ng/mL with low transferrin saturation suggest combined iron deficiency and anemia of chronic disease. 1

Absolute Indications for IV Iron (First-Line Therapy)

IV iron is mandatory as first-line treatment in the following scenarios:

• Active inflammatory bowel disease with hemoglobin < 10 g/dL, because inflammation-driven hepcidin severely impairs oral iron absorption. 1
• Post-bariatric surgery patients, due to disrupted duodenal iron absorption mechanisms. 1
• Chronic kidney disease patients on hemodialysis, where IV iron is the preferred route. 1, 3
• Intolerance to ≥ 2 different oral iron formulations (e.g., ferrous sulfate and ferrous fumarate). 1
• Failure of ferritin to improve after 4 weeks of compliant oral therapy. 1

Relative Indications for IV Iron

• Celiac disease with inadequate response to oral iron despite strict gluten-free diet adherence. 1
• Chronic heart failure with iron deficiency (ferritin < 100 ng/mL or 100–300 ng/mL with transferrin saturation < 20%), where IV iron improves symptoms and quality of life. 1, 4
• Ongoing gastrointestinal blood loss exceeding oral replacement capacity. 1
• Severe anemia (hemoglobin < 10 g/dL) requiring rapid correction, particularly with transferrin saturation < 20%. 5

Treatment Targets After IV Iron

• Ferritin ≥ 100 ng/mL to ensure adequate iron stores and prevent rapid recurrence. 1, 5
• Transferrin saturation ≥ 20% to confirm iron availability for erythropoiesis. 1, 3
• Hemoglobin increase of ≈ 2 g/dL within 3–4 weeks is the expected response. 1

Special Population Considerations

Chronic Kidney Disease (Non-Dialysis)

• Start iron when transferrin saturation ≤ 30% AND ferritin ≤ 500 ng/mL in patients not receiving erythropoiesis-stimulating agents. 1
• In CKD with hemoglobin < 11 g/dL, maintain ferritin ≥ 100 ng/mL and transferrin saturation ≥ 20%. 1

Inflammatory Bowel Disease

• Re-initiate iron therapy when ferritin drops below 100 ng/mL or hemoglobin falls below 12 g/dL (women) or 13 g/dL (men). 1

Menorrhagia with Severe Anemia

• IV iron is first-line when hemoglobin < 10 g/dL with transferrin saturation < 20%, as ongoing blood loss exceeds oral replacement capacity. 5
• Maintenance IV iron every 3–6 months is typically required until definitive menorrhagia treatment. 5

Preferred IV Iron Formulations

• Ferric carboxymaltose: 750–1000 mg per 15-minute infusion; two doses ≥ 7 days apart provide 1500 mg total. 1
• Ferric derisomaltose: 1000 mg as a single infusion. 1
• Avoid iron dextran as first-line due to higher anaphylaxis risk (0.6–0.7%). 1

Critical Pitfalls to Avoid

• Do not use ferritin alone to diagnose iron deficiency in inflammatory conditions; always combine with transferrin saturation. 1, 3
• Do not apply general population ferritin cutoffs (< 15 ng/mL) to patients with chronic disease; use the higher threshold of < 100 ng/mL. 1, 3
• Do not continue oral iron beyond 4 weeks without hemoglobin improvement; switch to IV iron. 1
• Do not use oral iron in active IBD with hemoglobin < 10 g/dL; IV iron is mandatory. 1