Platelet alloantibodies in transfused patients

BACKGROUND: Patients receiving cellular blood components may form HLA antib odies and platelet-specific alloantibodies. STUDY DESIGN AND METHODS: Serum samples from a cohort of 252 patients with hematologic or oncologic diseases who are receiving cellular blood componen ts were studied for platelet-reactive antibodies. Specificity of platelet a lloantibodies was determined with a panel of typed platelets RESULTS: Platelet-reactive antibodies were defected in the sera of 113 pati ents (44.8% of 252), HLA antibodies in the sera of 108 (42.9%), and platele t-specific antibodies in the sera of 20 (8%). The following platelet-specif ic antibodies were identified: anti-HPA-5b (n = 10), anti-HPA-Ib (n = 4), a nti-HPA-5a (n = 2), anti-HPA-1a (n = 1), anti-HPA-2b (n = 1), anti-HPA-1b+5 b (n = 1), and anti-HPA-1b+2b (n = 1). (n = 1). Fifteen sera from the 108 p atients with anti-HLA (13.9%) contained additional platelet-specific alloan tibodies, while in 5 sera, platelet-specific alloantibodies only were detec ted: anti-HPA-Sb (n = 4) and anti-HPA-fa (n = 1). Of the 108 sera with HLA antibodies, 29 (26.9%) showed discordant results when studied with the lymp hocytotoxicity test and the glycoprotein-specific immunoassay. Ten sera con tained panreactive antibodies against platelet glycoproteins (GP) IIb/IIIa, GPIa/IIa, and/or GPIb/IX. Alloimmunization occurred in 58.3 percent of fem ale patients with previous pregnancies, but in only 23.3 percent of those w ithout previous pregnancies (p = 0.0049). CONCLUSION: Platelet alloantibody specificities in transfused patients (pre dominantly anti-HPA-5b and -1b with antigen frequencies < 30% among whites) differ significantly from those observed in patients with neonatal alloimm une thrombocytopenia or posttransfusion purpura, in whom anti-MPA-1a (antig en frequency > 95%) is the most prevalent specificity. HLA antibody defecti on yields discordant results when the lymphocytotoxicity assay and a glycop rotein-specific immunoglobulin-binding assay are used.