In the initial workup of anemia, which single laboratory parameter best differentiates iron deficiency anemia from anemia of chronic disease?

Explanation

## Serum Ferritin as the Key Discriminator **Key Point:** Serum ferritin is the most reliable single parameter to differentiate iron deficiency anemia (IDA) from anemia of chronic disease (ACD) in the initial workup. ### Why Ferritin Wins Serum ferritin reflects total body iron stores. In IDA, ferritin is **low** (typically <15 ng/mL), whereas in ACD, ferritin is **normal or elevated** (>100 ng/mL) because iron is sequestered in macrophages and not available for erythropoiesis. ### Comparative Laboratory Profile | Parameter | Iron Deficiency Anemia | Anemia of Chronic Disease | |-----------|------------------------|---------------------------| | **Serum Ferritin** | **Low (<15 ng/mL)** | **Normal/High (>100 ng/mL)** | | Serum Iron | Low | Low | | TIBC | High | Normal/Low | | Transferrin Saturation | Low | Low | | Bone Marrow Iron | Absent | Present | **High-Yield:** While serum iron and TIBC are both abnormal in IDA, they are also affected by inflammation and infection (which elevate ferritin). Ferritin is the most robust discriminator because it directly reflects iron stores. **Clinical Pearl:** A ferritin <15 ng/mL in a patient with microcytic anemia essentially confirms iron deficiency; a ferritin >100 ng/mL makes IDA very unlikely and points toward ACD, thalassemia trait, or sideroblastic anemia. **Warning:** Ferritin is an acute-phase reactant and can be falsely elevated in inflammation, infection, malignancy, and liver disease—but in the context of microcytic anemia with low serum iron and high TIBC, a high ferritin still favors ACD over IDA.