Neonatal alloimmune thrombocytopenia due to HPA-3a antibodies: a case report

A healthy infant was born at term by elective cesarean section to a 32-year-old para 4, gravida 4, mother. Within 24 hours, the infant was noted to have fairly extensive bruising on the back and shoulders. A full blood count evaluation was remarkable for severe thrombocytopenia (platelet count of 29 × 10⁹/L). Other hematologic parameters were normal. Human leukocyte antigen (HLA) class-1 antibodies but not platelet-specific antibodies were detectable in the maternal serum using a commerical antigencapture ELISA (GTI-PakPlus kit^®). Anti-HPA-3a antibodies, while weakly reactive in the monoclonal antibody immobilization of platelet antigens (MAIPA) assay in the immediate postpartum serum, were readily detectable using this assay in a sample taken 4 weeks later. Genotyping for human platelet antigens (HPA) 1–5 by the polymerase chain reaction technique with sequence-specific primers (PCR-SSP) revealed the infant’s platelet genotype to be HPA-1a/1a, 3a/3b, while that of the mother was HPA-1a/1a, 3b/ 3b, consistent with a diagnosis of anti-HPA-3a neonatal alloimmune thrombocytopenia (NAIT). This case illustrates the increased sensitivity of the MAIPA technique for the detection of plateletspecific antibodies. We believe this to be the first serologically confirmed case of NAIT due to anti-HPA-3a to be reported in the republic of Ireland. Immunohematology 2002;18:33–36.