Which of the following laboratory findings is characteristic of hereditary elliptocytosis?

Explanation

## Hereditary Elliptocytosis: Clinical and Laboratory Features **Key Point:** Hereditary elliptocytosis (HE) is a membrane disorder characterized by the presence of elliptical (oval) or rod-shaped RBCs on blood smear, but most patients have normal osmotic fragility and mild or no hemolysis. ### Comparison: Hereditary Spherocytosis vs. Hereditary Elliptocytosis | Feature | Hereditary Spherocytosis | Hereditary Elliptocytosis | | --- | --- | --- | | RBC morphology | Spherocytes (dense, round) | Elliptocytes (oval, rod-shaped) | | Osmotic fragility | **Increased** (lyse at higher saline) | **Normal** (lyse at normal saline) | | Hemolysis severity | Moderate to severe | Mild or absent in most cases | | Splenic involvement | Significant sequestration | Minimal | | Jaundice | Common | Rare | | Gallstones | Frequent | Uncommon | **High-Yield:** The critical distinguishing feature is **osmotic fragility**: - **HS:** Increased osmotic fragility (spherocytes cannot accommodate swelling) - **HE:** Normal osmotic fragility (elliptocytes retain membrane flexibility despite abnormal shape) ### Pathophysiology of Hereditary Elliptocytosis 1. Defect in spectrin (α or β chain) or protein 4.1 2. Reduced lateral linkage between spectrin molecules 3. RBCs deform into elliptical shape during passage through microvasculature 4. Shape change is **reversible** (unlike spherocytes) 5. Most HE patients are asymptomatic or have mild hemolysis **Clinical Pearl:** Hereditary elliptocytosis is often an **incidental finding** on routine blood smear. Many patients are completely asymptomatic and require no treatment. Hemolysis occurs only in a minority of cases (hereditary pyropoikilocytosis is a severe variant). **Mnemonic:** **EH-Normal** — Elliptocytosis, Hereditary = Normal osmotic fragility (in contrast to HS). ### Why Osmotic Fragility Distinguishes the Two - **Spherocytes (HS):** Already lost membrane surface area → cannot swell further → lyse at higher (less hypotonic) saline concentrations - **Elliptocytes (HE):** Retain normal membrane surface area and flexibility → can swell normally → lyse at normal saline concentrations **Warning:** Do not confuse HE with HS based on morphology alone — the osmotic fragility test is essential for diagnosis. Elliptocytes can also be seen in thalassemia and other conditions, but the normal osmotic fragility in HE is pathognomonic.