Iron requirement formula
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Ganzoni formula iron requirement calculation iron deficiency anemia
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Here is a complete breakdown of the iron requirement formula:
Iron Requirement Formula (Ganzoni Formula)
Total Iron Dose (mg) = Actual Body Weight (kg) × [Target Hb - Actual Hb (g/dL)] × 2.4 + Iron Stores (mg)
As confirmed by the [Washington Manual of Medical Therapeutics](the textbook source), this is the standard formula used clinically to estimate total IV iron replacement needs.
Components Explained
| Component | Value / Explanation |
|---|---|
| Actual body weight | In kg |
| Target Hb | Usually 14 g/dL for adults (some use 15 g/dL); use 13 g/dL for men or 12 g/dL for women if conservative |
| Actual Hb | Patient's current hemoglobin in g/dL |
| Factor 2.4 | Derived from: blood volume (~70 mL/kg) × iron content of Hb (3.4 mg/g Hb) × 0.001 (unit conversion) |
| Iron stores | 500 mg for adults ≥35 kg; 15 mg/kg for patients <35 kg; sometimes omitted if only correcting anemia without replenishing stores |
How the Factor 2.4 Is Derived
- Blood volume ≈ 70 mL/kg
- 1 dL blood contains ~0.034 g Hb (per unit Hb deficit × blood volume)
- Iron in Hb = 3.4 mg per gram of Hb
- 70 mL/kg × 3.4 mg/g ÷ 100 = 2.38 ≈ 2.4
(Some sources use 2.145 with a blood volume of 65 mL/kg instead of 70 mL/kg)
Worked Example
Patient: 60 kg adult, Hb = 7 g/dL, Target Hb = 14 g/dL
Total iron = 60 × (14 - 7) × 2.4 + 500 = 60 × 7 × 2.4 + 500 = 1008 + 500 = 1508 mg
Special Populations
| Population | Modification |
|---|---|
| Weight <35 kg | Iron stores = 15 mg/kg (not 500 mg) |
| Pregnant | Target Hb = 11 g/dL |
| CKD | Target Hb = 11-12 g/dL |
| Children | Use 15 mg/kg formula; target Hb ~13 g/dL |
Alternatively (Iron Dextran-Specific Formula)
Some references simplify for iron dextran (INFeD) dosing:
Hgb Iron Deficit (mg) = Weight (kg) × (14 - Hgb) × 2.145
Where 2.145 = 3.3 mg Fe/g Hb × 0.65 (blood volume fraction of body weight).
Source: - The Washington Manual of Medical Therapeutics, p. 799
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