Background: Thrombocytopenia has been shown to be present in about 1% of unselected newborns. Alloantibodies to platelets induce the most severe thrombocytopenia.
Material and methods: Samples from 195 mothers who had just given birth to thrombocytopenic children, were analysed by platelet antigen genotyping and detection of platelet specific antibodies.
Results: 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.
Interpretation: 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.