Schistocytes

Schistocytes form when RBCs are mechanically sheared as they pass through damaged or occluded microvasculature, or through abnormal mechanical surfaces such as prosthetic heart valves. Key causes include thrombotic microangiopathies—thrombotic thrombocytopenic purpura (TTP), hemolytic uremic syndrome (HUS), disseminated intravascular coagulation (DIC)—as well as HELLP syndrome, malignant hypertension, and mechanical hemolysis from prosthetic valves or severe vasculitis. Pathophysiology involves fibrin strand deposition in small vessels or turbulent flow across damaged surfaces, causing RBCs to fragment as they squeeze through narrowed or obstructed lumens. Clinically, schistocytes accompany signs of hemolysis: elevated LDH, low haptoglobin, indirect hyperbilirubinemia, and reticulocytosis. In TTP/HUS, schistocytes are seen alongside thrombocytopenia (due to platelet consumption in microthrombi) with a classic pentad (in TTP): fever, renal dysfunction, neurologic symptoms, thrombocytopenia, and MAHA. In DIC, schistocytes occur with consumptive coagulopathy, prolonged PT/PTT, low fibrinogen, and elevated D-dimer. Diagnosis requires correlating peripheral smear findings with clinical context and laboratory studies; management targets the underlying cause (e.g., plasma exchange for TTP, treatment of underlying infection/malignancy for DIC, delivery for HELLP syndrome). This is a classic high-yield smear finding for boards, often tested in questions requiring differentiation of hemolytic anemias.