## Distinguishing Iron Deficiency Anemia from Anemia of Chronic Disease ### Key Laboratory Discriminator **Key Point:** Serum ferritin is the single best discriminating feature between iron deficiency anemia (IDA) and anemia of chronic disease (ACD). ### Comparative Table | Feature | Iron Deficiency Anemia | Anemia of Chronic Disease | | --- | --- | --- | | **Serum Ferritin** | **Low (<30 ng/mL)** | **Normal or elevated (>100 ng/mL)** | | Serum Iron | Low | Low | | TIBC | Elevated | Normal or low | | Transferrin Saturation | Low (<16%) | Low | | Hemoglobin | Variable | Variable | | MCV | Microcytic (early) | Normocytic (usually) | | Reticulocyte Count | Low (relative) | Low (relative) | | Bone Marrow Iron | Absent | Present | ### Pathophysiology **High-Yield:** In IDA, total body iron stores are depleted, so ferritin is genuinely low. In ACD, iron is sequestered in macrophages due to elevated hepcidin (from IL-6 in chronic inflammation), so ferritin is normal or high because ferritin is an acute phase reactant. ### Why Ferritin Wins 1. **Hemoglobin and MCV** are non-specific; both conditions can present with overlapping values. 2. **Reticulocyte count** is similarly suppressed in both conditions due to inadequate erythropoietin response. 3. **Serum ferritin** directly reflects total body iron stores and is the gold standard discriminator. **Clinical Pearl:** When ferritin is borderline (30–100 ng/mL), use transferrin saturation or bone marrow iron staining to confirm IDA. **Mnemonic:** **FERRITIN = IRON STORES** — Low ferritin = depleted iron (IDA); high ferritin = sequestered iron (ACD).
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