Diseases of Platelet Number: Immune Thrombocytopenia, Neonatal Alloimmune Thrombocytopenia, and Posttransfusion Purpura

Immune-mediated platelet disorders disrupt normal regulation of platelet number because of antibody-mediated or cell-mediated platelet destruction or platelet underproduction. Antibodies that target self (autoimmune) or nonself (alloimmune) antigens on platelets can cause severe thrombocytopenia. Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by antibodies directed against platelet glycoproteins (GPs). Neonatal alloimmune thrombocytopenia (NAIT) is a thrombocytopenic syndrome caused by platelet alloantibodies. Posttransfusion purpura (PTP) has features of both alloantibody- and autoantibody-mediated processes. The pathophysiology, clinical manifestations, and management of these disorders are discussed in this chapter.