When are iron infusions recommended for patients with iron deficiency anemia, particularly those with chronic diseases such as kidney disease, inflammatory bowel disease, or cancer?

Iron Infusions: When to Recommend

Intravenous iron should be used as first-line treatment in patients with iron deficiency anemia who have oral iron intolerance, failed oral iron therapy (no ferritin improvement), hemoglobin below 10 g/dL, clinically active inflammatory disease, or conditions where oral absorption is compromised. 1

Primary Indications for IV Iron

Absolute Indications

• Oral iron intolerance or failure: When patients cannot tolerate oral iron or ferritin levels do not improve after an adequate trial 1
• Severe anemia: Hemoglobin below 10 g/dL (100 g/L) 1
• Malabsorption conditions: Post-bariatric surgery patients, particularly those with disrupted duodenal absorption 1
• Need for erythropoiesis-stimulating agents (ESAs): IV iron enhances ESA response 1

Disease-Specific Recommendations

Inflammatory Bowel Disease (IBD)

IV iron is first-line therapy when:

• Active inflammation is present with compromised absorption 1
• Hemoglobin is below 10 g/dL 1
• Previous oral iron intolerance 1
• Clinically active disease regardless of hemoglobin level 1

Oral iron may be considered only when:

• Disease is clinically inactive 1
• Mild anemia (Hb 11.0-12.9 g/dL in men, 11.0-11.9 g/dL in women) 1
• No previous oral iron intolerance 1

The rationale: IV iron is more effective, shows faster response, and is better tolerated than oral iron in IBD 1. Oral iron may exacerbate intestinal inflammation and alter microbiota 1.

Chronic Kidney Disease (CKD)

IV iron is preferred for:

• All hemodialysis patients (CKD stage 5D) 2
• Non-dialysis CKD patients with functional iron deficiency (TSAT ≤20% with ferritin >100 ng/mL) 2
• Patients receiving ESA therapy 2

Diagnostic thresholds differ in CKD:

• Absolute iron deficiency: TSAT ≤20% and ferritin ≤100 ng/mL (predialysis/peritoneal dialysis) or ≤200 ng/mL (hemodialysis) 2
• Functional iron deficiency: TSAT ≤20% with elevated ferritin, due to increased hepcidin 2

Cancer Patients

IV iron is indicated when:

• Iron homeostasis is impaired by proinflammatory cytokines and elevated hepcidin 1
• Functional iron deficiency is present (adequate stores but insufficient availability) 1
• Rapid iron supply is needed 3

Oral iron only considered when:

• Absolute iron deficiency (ferritin <100 ng/mL) AND non-inflammatory conditions (CRP <5 mg/L) 1

Heart Failure

IV iron improves exercise capacity in:

• NYHA class II/III heart failure patients with iron deficiency 4
• Dosing based on weight and hemoglobin level (see FDA label for specific regimens) 4
• Maintenance dosing at 12,24, and 36 weeks if ferritin <100 ng/mL or ferritin 100-300 ng/mL with TSAT <20% 4

Practical Administration Guidelines

Formulation Selection

Prefer high-dose formulations that allow 1-2 infusions over multiple-dose regimens 1:

• Ferric carboxymaltose: up to 1,000 mg per dose, 15-minute infusion 1, 4
• Ferric derisomaltose: up to 20 mg/kg per dose 1
• Iron isomaltoside: up to 1,000 mg per dose 1

Dosing Strategy

Simple weight-based dosing (more effective than Ganzoni formula) 1:

• Body weight <70 kg: 1,000-1,500 mg total (depending on Hb level)
• Body weight ≥70 kg: 1,500-2,000 mg total (depending on Hb level)
• Hb 10-12 g/dL (women) or 10-13 g/dL (men): 1,000-1,500 mg
• Hb 7-10 g/dL: 1,500-2,000 mg 1

Safety Considerations

All IV iron formulations have similar safety profiles 1:

• True anaphylaxis is very rare 1
• Most reactions are complement activation-related pseudo-allergy (infusion reactions), not true anaphylaxis 1
• No test dose required for modern formulations (except iron dextran) 1, 4
• Monitor serum phosphate in patients requiring repeat courses within 3 months 4

Monitoring and Retreatment

Follow-up Schedule

• IBD patients: Monitor every 3 months for at least 1 year after correction, then every 6-12 months 1
• General population: Check hemoglobin 3-monthly for 12 months, then 6-monthly for 2-3 years 1

Retreatment Triggers

Reinitiate IV iron when 1:

• Serum ferritin drops below 100 ng/mL, OR
• Hemoglobin falls below 12 g/dL (women) or 13 g/dL (men)

Common pitfall: Rapid recurrence of iron deficiency in asymptomatic IBD patients should raise suspicion for subclinical inflammatory activity 1.

When Oral Iron Is Acceptable

Oral iron (once daily dosing preferred) may be first-line when 1:

• Mild iron deficiency anemia
• No inflammatory conditions
• Clinically inactive disease
• No previous intolerance
• Time is not critical

Optimize oral iron absorption 1:

• Add vitamin C to improve absorption
• Once-daily or alternate-day dosing (better tolerated, similar absorption)
• Ferrous sulfate is preferred (least expensive, no advantage of other formulations)

The evidence strongly supports a lower threshold for IV iron use than historically practiced, particularly in chronic inflammatory conditions where oral iron is ineffective due to hepcidin-mediated functional iron deficiency 1.