schistocytes

Schistocytes are fragmented red blood cells characterized by irregular, often helmet-shaped fragments resulting from mechanical disruption of erythrocytes during intravascular hemolysis. They are sometimes referred to as helmet cells or fragmented cells. On a stained peripheral blood smear, schistocytes appear as irregularly shaped fragments with jagged or notched borders, lacking a normal central pallor.

Causes include microangiopathic hemolytic anemia (MAHA) due to conditions such as thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, disseminated intravascular coagulation, malignant hypertension, HELLP syndrome, and mechanical destruction from prosthetic heart valves or vascular devices. They arise when red cells traverse damaged or thrombus-laden microvasculature or are exposed to shear forces from prosthetic or stenotic valves, leading to fragmentation.

Diagnosis and laboratory correlation: Schistocytes on blood smear are a hallmark of MAHA and intravascular hemolysis. They are typically accompanied by elevated LDH, decreased haptoglobin, reticulocytosis, and a negative Coombs test (in non-autoimmune cases). The percentage or number of schistocytes can guide assessment of hemolysis severity but should be interpreted alongside other findings.

Clinical significance and management: The presence of schistocytes signals active intravascular hemolysis and prompts evaluation for MAHA and its underlying cause. Management focuses on treating the underlying condition (e.g., plasma exchange for TTP, supportive care for HUS, management of hypertension or valve pathology).