ADAMTS13 and thrombotic thrombocytopenic purpura: Thrombotic thrombocytopenic purpura (TTP) is a life-threatening form of thrombotic microangiopathy, characterized by microangiopathic hemolytic anemia (MAHA), thrombocytopenia, and neurological deficits, renal injury, and fever caused by the severe deficiency of plasma ADAMTS13 activity.