Frequencies of maternal platelet alloantibodies and autoantibodies in suspected fetal/neonatal alloimmune thrombocytopenia, with emphasis on human platelet antigen‐15 alloimmunization

Background and Objectives Serological evaluation of maternal sera for platelet antibodies in suspected fetal/neonatal alloimmune thrombocytopenia (FNAITP) discloses in only ≈ 30% of individuals a platelet‐specific antibody. Transfusion‐induced alloimmunization against human platelet antigen‐15 (HPA‐15) has been reported to be about as common as against HPA‐5, the second most common platelet antibody. Thus, anti‐HPA‐15 may also contribute significantly to yet‐unclear cases of FNAITP. Materials and Methods In this retrospective analysis, we provide data on maternal platelet antibodies from 309 mothers who delivered an offspring with suspected FNAITP. Results Genotyping maternal and paternal samples (together n  = 573) revealed a gene frequency of 0·496 for HPA‐15a and a gene frequency of 0·504 for HPA‐15b. HPA‐15 antibodies were detected in 2% of all samples. Anti‐HPA‐15a and ‐15b were detected in two and three samples, respectively. One serum reacted equally with HPA‐15a and ‐15b platelets. The most frequent platelet‐specific antibodies were anti‐HPA‐1a (22%), but anti‐HPA‐5b (8·4%) were more frequent than anti‐HPA‐15. In addition, panreactive (5·5%) or autoreactive (5·2%) anti‐GPIIb/IIIa or anti‐GPIb/IX were detectable in maternal samples. Conclusions These data indicate that HPA‐15 alloimmunization needs only to be considered in subjects with suspected FNAITP if no other platelet‐specific antibody is detectable. The presence of panreactive or autoreactive antibodies should also be considered in neonatal thrombocytopenia.