Importance of platelet serologic testing for defining the cause of neonatal thrombocytopenia

This report illustrates the importance of serologic techniques for defining the etiology of neonatal thrombocytopenia. In Case 1 the maternal count was low normal to normal during the first postpartum week. Several weeks later the appearance of persistent maternal thrombocytopenia led to the demonstration of anti-GP IIb-IIIa in stored and freshly obtained maternal sera, suggesting that the mother had an autoimmune type of thrombocytopenia. The mother of Case 2 had systemic lupus erythematosus. However, serologic testing revealed that the infant's thrombocytopenia was not related to the mother's lupus but was secondary to alloimmunization with the PlA1 antigen. An algorithm for defining etiologic mechanisms in infants with antibody-mediated forms of thrombocytopenia is presented.