Influence of HPA-1a and HLA antibodies on primary hemostasis.

The influence of platelet specific and HLA antibodies was investigated on primary hemostasis by the in vitro bleeding test (IVBT) (Thrombostat 4000). Seven of 12 plasmas with HPA-1a (P1A1) antibodies and two with antibodies against glycoprotein Ib/IX significantly inhibited the IVBT of normal, cross-match-positive donor blood. This correlated with a significant increase of GMP-140 (CD 62) on the platelets, determined by flow cytometry. These results agree with the literature showing both activation and inhibition of platelet function by platelet specific antibodies. On the other hand, HLA antibodies showed a similar platelet activation (shortening of occlusion time and decrease in blood volume in the IVBT, increase of CD 62 expression) as plasma samples of polytransfused thrombocytopenic patients without HLA antibodies. It can be concluded that neither an activating nor an inhibitory effect of HLA antibodies on platelet function is significant in vivo. The IVBT seems not to be suited for compatibility testing.