Answer is C (Idiopathic Thrombocytopenic Purpura (ITP)) Idiopathic Thrombocytopenic Purpura (ITP) is an immune complex mediated thrombocytopenia characterized by varying degrees of bleeding manifestations due to destruction of platelets. 1TP is not associated with an increased incidence of venous and/or aerial thrombosis. Paroxysmal Nocturnal Haemoglobinuria (PNH), Diseminated Intravascular Coagulation (DIC) and Heparin Induced Thrombocytopenia (HIT) are all associated with increased risk of venous and/or aerial thrombotic events. Risk factors for Thrombosis: Venous -- Venous and Aerial Inherited Inherited Factor V Leiden Homocystinuria Prothrombin G20210A Dysfibrinogenemia Antithrombin deficiency Protein S deficiency' Elevated F VIII Acquired Acquired Age Malignancy Previous thrombosis Antiphospholipid antibody syndrome (APLA) Immobilization Hormonal therapy Major surgery Polycythemia vera Pregnancy &puerperium Essential thrombocythemia Hospitalization Paroxysmal nocturnal hemoglobinuria (PNH) Obesity Thrombotic thrombocytopenic Purpura (TTP) Infection Heparin-induced thrombocytopenia (HIT) APC resistance, nogenetic Disseminated intravascular cogulation (DIC) Unknowndeg Mixed (Inherited and acquired) Elevated factor II, IX, XI Hyperhomocysteinemia Elevated TAFI levels Low levels of TFPI "Unknown whether risk is inherited or acquired. Note APC, activated protein C; TAFI. thrombin-activatable fibrinolysis inhibitor: TFPI, tissue factor pathway inhibitor. Note : Heparin induced Thrombocytopenia is more commonly associated with Thrombosis than Bleeding Heparin induced Thrombocytopenia is more commonly associated with Thrombosis than Bleeding Heparin induced thrombocytopenia should be included in the differential diagnosis of conditions that produce thrombosis despite thrombocytopenia. Despite thrombocytopenia bleeding is rare in HIT. On the contrary HIT is more related to thrombosis, which often leads to initial recognition of this condition (HIT). `Thrombosis often leads to initial recognition of HIT. Bleeding is rare despite thrombocytopenia' - Essentials of Emergency Medicine (2006)/286 Thrombocytopenia with Thrombosis DIC TTP HUS HIT Thrombosis in Heparin Induced Thrombocytopenia is caused by the generation of prothrombotic platelet micropaicles that promote thrombin generation. HIT is an antibody - mediated process that is triggered by antibodies directed against neoantigens on PF4 that are exposed when heparin binds to this protein. These antibodies (usually IgG type) bind simultaneously to heparin PF4 complex and to platelet Fc receptors. Such binding activates the platelets and generates platelet micropaicles. Circulating micropaicles are prothrombotic because they express anionic phospholipids on their surface and can bind clotting factors and promote thrombin generation. Features of Heparin-Induced Thrombocytopenia Features Details Thrombocytopenia Platelet count of <100,000/,uL or a decrease in platelet count > 50% Timing Platelet count falls 5-10 days after staing heparin Type of heparin More common with unfractionated heparin than with low-molecular-weight heparin Type of patient More common in surgical patients than medical patients; more common in women than in men. Thrombosis Venous thrombosis more common than aerial thrombosis