## Distinguishing AIHA from MAHA on Peripheral Smear ### Key Morphologic Difference: Spherocytes vs. Schistocytes **High-Yield:** The **predominant RBC abnormality** is the best smear discriminator: - **AIHA** → **Spherocytes** (immune-mediated loss of membrane, reduced surface area) - **MAHA** → **Schistocytes** (mechanical fragmentation from fibrin strands or turbulent flow) **Key Point:** While both conditions cause hemolysis and may show both spherocytes and schistocytes, the **predominant** finding differs: - In AIHA, spherocytes dominate because antibody-coated RBCs lose membrane and become spherical. - In MAHA, schistocytes dominate because RBCs are sheared by fibrin deposition or endothelial damage. ### Comparative Smear Features | Feature | AIHA | MAHA | Discriminatory? | |---------|------|------|------------------| | **Spherocytes** | **Predominant** | Few to absent | **Yes** | | **Schistocytes** | Few to absent | **Predominant** | **Yes** | | Polychromasia | Present | Present | No | | Reticulocytosis | Present | Present | No | | Helmet cells | Absent | Present | Yes | | Bite cells | Absent | Absent | No | **Clinical Pearl:** Spherocytes in AIHA are **osmotically fragile** (fail the osmotic fragility test), whereas schistocytes in MAHA are mechanically fragmented and have normal osmotic fragility. This pathophysiologic difference is reflected in smear morphology. ### Why Polychromasia and Schistocytes Are Not Discriminatory - **Polychromasia** and elevated reticulocyte count occur in both conditions (both are hemolytic). - **Schistocytes** can appear in AIHA if there is concurrent DIC or thrombotic microangiopathy, but they are not the predominant finding. - The **predominance** of spherocytes in AIHA vs. schistocytes in MAHA is the key distinction. ### Mnemonic **AIHA = Antibody → Spheres** (antibody coating → membrane loss → spherical shape) **MAHA = Mechanical → Shards** (mechanical shearing → fragmented RBCs) [cite:Robbins 10e Ch 13]
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