Immune thrombocytopenic purpura (ITP) is an autoimmune disorder characterized by low platelet count and mucocutaneous bleeding. The estimated incidence is 100 per 1 million persons per year. ITP can be a primary disorder or secondary to an underlying disorder and can have an acute (6 months or less) or chronic presentation. ITP in children and adults is very different. In children, the incidence is equal between boys and girls, who are usually in good health until they present with petechiae or purpura a few days or weeks after an acute infectious illness. In more than 70% of the cases, the illness resolves within 6 months. In adults, the illness is more chronic and insidious, and is more common in women.

The pathophysiology is related to autoantibodies against platelets, which then undergo accelerated clearance in the spleen. The diagnosis of ITP remains one of exclusion. Disorders that ITP occurs secondary to include systemic lupus erythematosus, antiphospholipid syndrome, immunodeficiency states such as common variable hypogammaglobulinemia and immunoglobulin A deficiency, lympho-proliferative disorders (chronic lymphocytic leukemia, large granular lymphocytic leukemia, and lymphoma), infection with human immunodeficiency virus and hepatitis C virus, and drugs such as heparin and quinidine.