spherocyte

Spherocytes arise when RBC membrane is lost without proportional loss of cytoplasm, causing cells to become sphere-shaped instead of biconcave discs. This occurs via two major mechanisms: (1) Hereditary spherocytosis - a genetic defect in membrane cytoskeletal proteins (ankyrin, spectrin, band 3, protein 4.2) causing progressive membrane loss and vesiculation; (2) Autoimmune hemolytic anemia (warm type, IgG-mediated) - splenic macrophages partially phagocytose antibody-coated RBC membrane, converting biconcave cells to spherocytes. Spherocytes have decreased surface-area-to-volume ratio, making them less deformable and more prone to destruction in the spleen (extravascular hemolysis), leading to splenomegaly. Lab findings include increased osmotic fragility test, increased mean corpuscular hemoglobin concentration (MCHC), and elevated reticulocyte count. Hereditary spherocytosis presents with hemolytic anemia, jaundice, splenomegaly, and increased risk of pigmented (calcium bilirubinate) gallstones; treatment is splenectomy in severe cases. Direct Coombs test differentiates AIHA (positive) from hereditary spherocytosis (negative). Peripheral smear is key to diagnosis - spherocytes appear as small, hyperchromic RBCs without central pallor, distinguishing them from normal biconcave RBCs and other poikilocytes like schistocytes or target cells.