Neonatal alloimmune thrombocytopenia.

Abstract

EONATAL alloimmune thrombocytopenia (NAIT) is a relatively rare disease, occurring in 1 in 3,000 to l in 5,000 births. 1.2 The platelet equivalent of hemolytic disease of the newbom, NAIT is the result of matemai alloimmunization against a platelet antigen present on fetal and pa­ ternal platelets but absent on matemai platelets. Although less common than matemai autoimmune thrombocytopenia, matemai alloimmunization leads to much more profound neonatal and perina­ tal thrombocytopenia, resulting in intracerebral hemorrhage and death or severe neurological se­ quelae in up to 30% of affected neonates. 2-4 Unlike red blood cell alloimmunization, NAIT affects the frrst bom infant in 60% of cases. Considerable progress has been made in the treatment of NAIT, therefore it is critical to consider this diagnosis in a thrombocytopenic infant. By analogy with Rh hemolytic disease of the newbom, there is much interest in understanding the immune response to platelet alloantigens, with the ultimate goal of pre­ venting NAIT. For reasons that are not well un­ derstood, only a small percentage of mothers ex­ posed to incompatible platelet antigens form alloantibodies resulting in NAIT. 1.5 This review examines the platelet-specific antigens and anti­ bodies implicated in NAIT, and the physiology of the immune response to HPA-la, the antigen most frequently implicated in NAIT. The laboratory and clinical features of NAIT as well as its treatment and possible prevention is also discussed.