Iron Correction Formula for Iron Deficiency Anemia
Use the simplified weight and hemoglobin-based dosing table rather than the Ganzoni formula, as it demonstrates superior efficacy, better compliance, and avoids calculation errors. 1
The Simplified Dosing Scheme (Preferred Method)
The European Crohn's and Colitis Organization (ECCO) recommends abandoning the traditional Ganzoni formula in favor of a simplified table-based approach that has proven more effective in clinical trials 1:
| Hemoglobin Level | Body Weight <70 kg | Body Weight ≥70 kg |
|---|---|---|
| 10-12 g/dL (women) or 10-13 g/dL (men) | 1000 mg | 1500 mg |
| 7-10 g/dL | 1500 mg | 2000 mg |
Important caveat: Patients with hemoglobin below 7.0 g/dL likely require an additional 500 mg beyond these recommendations 1.
Why This Approach Is Superior
The FERGIcor trial directly compared this simplified scheme against Ganzoni-calculated dosing and demonstrated better efficacy, compliance, and safety profile 1. The traditional Ganzoni formula—body weight (kg) × [target Hb - actual Hb (g/dL)] × 0.24 + 500—is inconvenient, prone to calculation errors, inconsistently applied in practice, and systematically underestimates iron requirements 1.
Route Selection Algorithm
Choose intravenous iron as first-line therapy in the following situations 1:
- Hemoglobin <10 g/dL (100 g/L)
- Clinically active inflammatory disease
- Previous intolerance to oral iron
- Need for erythropoiesis-stimulating agents
- Malabsorption conditions
Oral iron may be used only when ALL of the following criteria are met 1:
- Mild anemia (Hb 11.0-11.9 g/dL in women; 11.0-12.9 g/dL in men)
- Disease is clinically inactive
- No previous intolerance to oral iron
Oral Iron Dosing (When Appropriate)
Prescribe ferrous sulfate 200 mg once daily as the first-line oral regimen 2. Alternatively, alternate-day dosing (every other day) improves tolerability with similar or superior efficacy by allowing hepcidin levels to decrease between doses 2, 3.
- Take as a single morning dose on an empty stomach for optimal absorption 2
- Add vitamin C 500 mg with each dose to enhance absorption 2
- Continue for 3 months after hemoglobin normalizes to replenish iron stores 2, 4
Critical pitfall to avoid: Do not prescribe multiple daily doses—once-daily or alternate-day dosing is superior 2.
Monitoring Response
Recheck hemoglobin after 4 weeks of oral therapy 2, 4:
- Expect an increase of at least 1-2 g/dL if treatment is effective 1, 4
- If hemoglobin fails to rise adequately, switch to intravenous iron 2, 4
- Check hemoglobin and red cell indices every 3 months during active disease
- Every 6-12 months in patients with mild disease or remission
- Do not check ferritin immediately after IV iron (wait 8-10 weeks due to falsely elevated levels) 2
Iron Deficiency Without Anemia
For patients with iron deficiency but no anemia, consider 500-1000 mg total dose 1. While evidence for treating non-anemic iron deficiency in general populations is limited, this approach is reasonable based on extrapolation from other conditions 1.
Safety Thresholds
Upper limits for guiding therapy to avoid iron overload 1:
- Transferrin saturation >50%
- Serum ferritin >800 μg/L
The risk of iron overload in chronically bleeding patients is intrinsically low, but these thresholds should still be respected 1.
Diagnostic Context
Ferritin interpretation depends on inflammatory status 1:
- Without inflammation: ferritin <30 μg/L confirms iron deficiency
- With inflammation: ferritin up to 100 μg/L may still indicate iron deficiency
- Ferritin 30-100 μg/L with inflammation suggests combined iron deficiency and anemia of chronic disease