are formed by fibrin formation and entrapment of red blood cells leading to fragmentation due to the force of blood flow in the vessels. Disseminated intravascular coagulation Disseminated intravascular coagulation or DIC is caused by a systemic response to a specific condition including sepsis and severe infection, malignancy, obstetric complications, massive tissue injury, or systemic diseases. Disseminated intravascular coagulation is an activation of the coagulation cascade which is usually a result of an increased exposure to tissue factor. The activation of the cascade leads to thrombi formation which causes an accumulation of excess fibrin formation in the intravascular circulation. The excess fibrin strands cause mechanical damage to the red blood cells resulting in schistocyte formation and also thrombocytopenia and consumption of clotting factors. Schistocyte values between .5% and 1% are usually suggestive of DIC. Thrombotic thrombocytopenic purpura Thrombotic thrombocytopenic purpura or TTP is caused by primary platelet activation. Thrombotic thrombocytopenic purpura leads to increased amounts of large von Willebrand factor which then attach to activated platelets and mediate further platelet aggregation. Platelets end up being removed and the resulting fibrin strand formation remains. These fibrin strands along with the stress from the blood flow cause fragmentation of the red blood cells, leading to schistocyte formation. In TTP, a schistocyte count between 3–10% is common, but >1% is suggestive of the disease. Hemolytic-uremic syndrome Hemolytic-uremic syndrome or HUS is hemolytic anaemia, acute kidney failure (uremia), and thrombocytopenia. HUS is caused by E. coli bloody diarrhea and specific strains of shiga toxin. The bacteria in HUS cause damage to the endothelium which results in platelet activation and formation of microthrombi. Red cells get trapped in the fibrin strands of the microthrombi and become sheared by the force of blood flow leading to schistocyte formation. Malfunctioning cardiac valves Leaky prosthetic heart valves and other cardiac assisted devices can lead to microangiopathic hemolytic anemia (with schistocyte formation) and thrombocytopenia. The force from the blood flow over the high pressure gradient from the prosthesis leads to fragmentation of red cells, and schistocyte formation. This is rare and only occurs in about 3% of patients. References External links Images in Clinical Medicine: Hemolytic Anemia after Mitral-Valve Repair, Sarinya Puwanant and Watchara Lohawijarn, N Engl J Med 2012; 367:e29 (November 15, 2012) DOI: 10.1056/NEJMicm1201695 [FREE TEXT] Abnormal clinical and laboratory findings for RBCs