This is a general category that contains two diseases: Thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) and may also be associated with hematopoietic stem cell transplant and various drugs (such as clopidogrel and ticlopidine). The “thrombotic” portion of the name comes from the fact that these disorders are secondary to clotting of blood components, while “microangiopathy” refers to damage to small blood vessels. So, patients with TMAs have blood clots/aggregates (usually composed of platelets) in small blood vessels, leading to damage to the vessels and the the red blood cells that try to squeeze past the thrombi. See the individual diseases for more information.