Immune thrombocytopenic purpura: A blood disorder characterized by the destruction of blood platelets due to the presence of antiplatelet autoantibodies. (Autoantibodies are antibodies directed against the patient's own cells, in this disorder, the patient's own platelets.) Thrombocytopenia refers to a decrease in platelets (also known as thrombocytes). Purpura pertains to the visible hallmarks: purplish areas in the skin and mucous membranes (such as the mouth lining) where bleeding has occurred as a result of decreased platelets.
Immune thrombocytopenic purpura (ITP) can be triggered by drugs, or associated with infection, pregnancy, or immune disorders such as systemic lupus erythematosus. About half of all cases are classified as "idiopathic," meaning the cause is unknown. The abbreviation "ITP" is much used. It stands for both immune thrombocytopenic purpura and idiopathic thrombocytopenic purpura.