Platelet-specific antibodies in HLA-immunized patients receiving chronic platelet support

BACKGROUND : In HLA‐alloimmunized patients, the unexpected failure of HLA‐matched platelet transfusions usually raises the suspicion about concomitant platelet‐specific antibodies. As the reported frequency of platelet‐specific antibodies in multitransfused patients varies widely, the aim of this study was to determine the prevalence of such antibodies in a population of chronic thrombocytopenic patients with HLA antibodies. STUDY DESIGN AND METHODS : From 1985 to 1997, 11,777 determinations of HLA antibodies were performed in 1330 hematologic patients receiving chronic platelet support. Fifty‐two patients with HLA alloimmu‐nization that lasted more than 1 month were selected. The search for platelet‐specific antibodies was performed by using a monoclonal antibody immobilization of platelet antigens assay, thus allowing the identification of platelet‐specific antibodies directed against the platelet glycoproteins (GP) Ib/IX, GPIIb/IIIa, and GPIa/IIa. Specificity of the platelet‐specific antibodies was further investigated by using a solid‐phase assay with chloroquine‐treated platelets. RESULTS : Only 2 (3.8%) of the 52 patients had platelet‐specific antibodies. One antibody reacted with an epitope of the GPIIb/IIIa that was present in all the panel platelets, and that probably was an autoantibody. The other was an anti‐HPA‐5b. CONCLUSIONS : The prevalence of platelet‐specific antibodies in patients with HLA alloimmunization is very small. The search for concomitant platelet‐specific antibodies would be indicated only when other causes of refractoriness to HLA‐matched platelets are ruled out.