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 approximately 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.