[Significance of maternal alloantibodies for neonatal thrombocytopenia]

Thrombocytopenia has been shown to be present in about 1% of unselected newborns. Alloantibodies to platelets induce the most severe thrombocytopenia.

Samples from 195 mothers who had just given birth to thrombocytopenic children, were analysed by platelet antigen genotyping and detection of platelet specific antibodies.

75 mothers were typed human platelet antigen (HPA) 1bb, and in 65 mother, anti-HPA 1a antibodies could be detected. Anti-HPA 5b antibodies were detected in three samples and anti-HLA antibodies in 73 samples.

Alloantibodies were shown to be an important cause of thrombocytopenia in the new-born children and anti-HPA 1a antibodies were, as expected, the most common platelet-specific antibody involved. Anti-HLA class 1 antibodies were detected as the only antibody in 51 cases of thrombocytopenia. Though it is not yet formally shown, this may indicate that anti-HLA class 1 antibodies may cause thrombocytopenia in the fetus and new-born. Based on the assumption that neonatal alloimmune thrombocytopenia is present in 1:1,000 new-born, 25% of the neonatal alloimmune thrombocytopenia cases in Norway are verified by laboratory analysis. Alloantibodies to thrombocytes are of clinical importance in future pregnancies and transfusions. The cost and benefit of a national screening program for anti-HPA 1a antibodies in all pregnant women should be carefully considered.