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

BACKGROUND: in HLA-alloimmunized patients, the unexpected failure of HLA-ma tched platelet transfusions usually raises the suspicion about concomitant platelet-specific antibodies. As the reported frequency of platelet-specifi c antibodies in multitransfused patients varies widely, the aim of this stu dy was to determine the prevalence of such antibodies in a population of ch ronic thrombocytopenic patients with HLA antibodies. STUDY DESIGN AND METHODS: From 1985 to 1997, 11,777 determinations of HLA a ntibodies were performed in 1330 hematolagic patients receiving chronic pla telet support. Fifty-two patients with HLA alloimmunization that lasted mor e than 1 month were selected. The search for platelet-specific antibodies w as performed by using a monoclonal antibody immobilization of platelet anti gens assay, thus allowing the identification of platelet-specific antibodie s directed against the platelet glycoproteins (GP) Ib/IX, GPIIb/IIIa, and G PIa/IIa. Specificity of the platelet-specific antibodies was further invest igated 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 wit h HLA alloimmunization is very small. The search for concomitant platelet-s pecific antibodies would be indicated only when other causes of refractorin ess to HLA-matched platelets are ruled out.