## Morphologic Classification of Anemias **Key Point:** The morphologic classification of anemias is based on **mean corpuscular volume (MCV)**, which reflects the average size of red blood cells. This is the primary parameter used in the initial laboratory workup of any anemia. ### MCV-Based Classification | Classification | MCV Range | Common Causes | | --- | --- | --- | | **Microcytic** | <80 fL | Iron deficiency, thalassemia, sideroblastic anemia, anemia of chronic disease (early) | | **Normocytic** | 80–100 fL | Hemolytic anemia, acute hemorrhage, hemoglobinopathies, aplastic anemia | | **Macrocytic** | >100 fL | B12 deficiency, folate deficiency, alcohol, reticulocytosis | **High-Yield:** MCV is the single most useful parameter for initial classification and differential diagnosis of anemia. It guides the next step in investigation (iron studies, B12/folate levels, reticulocyte count, hemolysis workup). **Mnemonic: MICROCYTIC ANEMIAS — "TAILS"** - **T**halassemia - **A**nemia of chronic disease - **I**ron deficiency - **L**ead poisoning (sideroblastic) - **S**ideroblastic anemia ### Why Other Parameters Are Secondary - **MCH (Mean Corpuscular Hemoglobin):** Reflects hemoglobin content per RBC; correlates with MCV but is not the primary classifier - **RDW (Red Cell Distribution Width):** Measures variation in RBC size; useful for detecting mixed anemias but not the primary morphologic classifier - **Hemoglobin concentration:** Defines anemia severity, not cell size
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