Marked thrombocytopenia in a neonate is associated with anti-HPA-5b, anti-HLA-A31, and anti-HLA-B55 antibodies.

Maternal antibodies against human platelet antigen (HPA) and/or human leukocyte antigen (HLA) cause fetal and neonatal alloimmune thrombocytopenia (FNAIT) in 0.09-0.15% of live births. Severe cases account for 5-31% and the frequency of multiple kinds of alloantibodies is 6.9-9% of FNAIT. We present a case of severe FNAIT associated with anti-HPA-5b, anti-HLA-A31, and anti-HLA-B55 antibodies, successfully treated with immunoglobulin and platelet transfusion. The anti-HLA-B55 antibody was detected in the newborn's serum, but disappeared on the 20th day, which was followed by an increase of the platelet count. These findings suggested the potential involvement of an anti-HLA antibody in the pathogenesis of FNAIT.