Anti-HPA-3A induces severe neonatal alloimmune thrombocytopenia

Objective: Fetal and neonatal alloimmune thrombocytopenia (AIT) caused by f ete-maternal incompatibility at the HPA-la (PLA-I) locus is well characteri zed. Alloimmunization and disease caused by HPA-3a is rare. Study design: We conducted a retrospective analysis of all known cases of A IT caused by HPA-3a incompatibility identified at 3 major reference laborat ories from 1986 to 1996. Platelet antigen typing and antibody specificity w ere determined by serologic evaluation. In some cases confirmatory genotypi ng was performed. Results: Fourteen cases of anti-HPA-Sa-induced AIT in 11 families were iden tified. Five patients had a previous affected sibling, and 2 cases were fir stborn children. All patients had severe thrombocytopenia at birth (platele t count <20 x 10(9)/L). Regardless of therapy, the median time to platelet recovery was 6 days (range, 3 to 23 days). Two (15%) patients had documente d intracranial hemorrhage, 1 with severe sequelae including apnea and convu lsions. A literature review describing 16 additional patients corroborates the finding of severe thrombocytopenia and a significant incidence of intra cranial hemorrhage caused by HPA-3a incompatibility. Conclusion: AIT caused by incompatibility of HPA-3a is similar in severity to disease caused by incompatibility of HPA-la. Affected families should be appropriately counseled and considered for antenatal therapy.