Thrombotic microangiopathy, not elsewhere classified

**Definition:** Thrombotic microangiopathies are microvascular occlusive disorders characterised by systemic or intrarenal aggregation of platelets, thrombocytopenia, and mechanical injury to erythrocytes. Thrombotic thrombocytopenic purpura (TTP) and haemolytic–uremic syndrome (HUS) represent a spectrum of thrombotic microangiopathies. In TTP, systemic microvascular aggregation of platelets causes ischemia in the brain and other organs. In HUS, platelet–fibrin thrombi predominantly occlude the renal circulation.