Causes of thrombocytopenia: I. -Decreased production of platelets: 1)selective impairment of platelet production: a)drug induced : alcohol , thiazides . b) Infections : measles, HIV .Disseminated intravascular coagulation (DIC) occurs as a complication of a wide variety of disorders. DIC is caused by the systemic activation of coagulation and results in the for- mation of thrombi throughout the microcirculation. As a conse- quence, platelets and coagulation factors are consumed and, secondarily, fibrinolysis is activated. Thus, DIC can give rise to either tissue hypoxia and microinfarcts caused by myriad microthrombi or to a bleeding disorder related to patho- logic activation of fibrinolysis and the depletion of the ele- ments required for hemostasis (hence the term consumptive coagulopathy). This entity probably causes bleeding more commonly than all of the congenital coagulation disorders combined. 2)nutritional deficiency: B12 and folate deficiency. 3) Bone marrow failure: aplastic anemia 4) Bone marrow replacement: Leukemia , disseminated cancer 5)Infective hematopoiesis:MDS II. -Decreased platelet survival 1) immunologic destruction: a)primary autoimmune:a/c & c/c immune thrombocytopenic purpura. b) secondary autoimmune:SLE, B-cell lymphoid neoplasms, Alloimmune , drug induced : (quinidine , heparin ,sulfa compounds.),infections:HIV , IMN. 2)non immunologic destruction: DIC, thrombotic microangiopathies , giant hemangiomas. III.- Sequestration: Hypersplenism IV. -Dilution :Transfusions Ref :Robbins pathologic basis of disease ; south east asia edition-9 ;pg450:table: 14-9.