All of the following are characteristic features of microcytic anemias EXCEPT:

Explanation

## Microcytic Anemias: Characteristic Features **Key Point:** Microcytic anemias are defined by MCV <80 fL and are primarily caused by iron deficiency, thalassemia, sideroblastic anemia, and anemia of chronic disease (ACD). ### Analysis of Each Option | Feature | Iron Deficiency | Thalassemia Trait | ACD | Sideroblastic | | --- | --- | --- | --- | --- | | MCV | <80 fL | <80 fL | <80 fL | <80 fL | | RDW | ↑ (high) | Normal | Normal | Normal | | Reticulocyte count | Low | Normal/High | Low | Low | | Serum ferritin | ↓ (low) | Normal | ↑ (high) | ↑ (high) | **High-Yield:** In iron deficiency anemia, RDW is characteristically elevated because of the wide variation in red cell sizes (anisocytosis) as iron becomes depleted. This is one of the earliest laboratory changes. **Clinical Pearl:** Anemia of chronic disease shows a paradoxical pattern — despite adequate iron stores (high ferritin), iron is sequestered in macrophages due to elevated hepcidin. This is why serum ferritin is elevated, not decreased. ### Why Option 3 Is Wrong Increased serum ferritin is NOT a feature of microcytic anemias in general — it is specific to ACD and sideroblastic anemia. In iron deficiency anemia (the most common microcytic anemia), ferritin is **low**, not high. The stem asks for a feature true of microcytic anemias broadly, and ferritin elevation contradicts the iron deficiency pattern. **Mnemonic:** **TAILS** — Thalassemia, ACD, Iron deficiency, Lead poisoning, Sideroblastic anemia (causes of microcytosis). Only ACD and sideroblastic have high ferritin.