Anti-leucocyte antibodies in platelet apheresis donors with and without prior immunizing events: implications for TRALI prevention

Background and Objectives Transfusion‐related acute lung injury (TRALI) prevention strategies in platelet (PLT) apheresis donors focus on identifying antileucocyte antibody‐positive donors. The use of microbead based assays for screening purposes is hampered by the lack of a consensus cut‐off for TRALI prevention and the undefined role of anti‐leucocyte antibodies in never‐alloexposed donors. This study evaluated anti‐leucocyte antibody assays in PLT apheresis donors with and without prior immunizing events with special focus on microbead assay cut‐offs, antibody specificities and their potential significance in never‐alloexposed donors. Material and Methods Blood samples of male and female PLT apheresis donors with and without history of prior immunization were tested for anti‐leucocyte antibodies. Results Of 262 female and 118 male PLT apheresis donors, 37·4% had prior immunizing events. Fifty‐eight of 238 (24·4%) donors without prior immunizing event had anti‐HLA antibodies confirmed in microbead single antigen assay (mean fluorescence intensity (MFI) >500). Even with a cut‐off MFI >3000, anti‐HLA antibodies were detected in 10·6% of female and 4·3% of male donors without history of immunization. Of the antibody specificities found, 6 of 17 (35·3%) anti‐HLA‐A, 4 of 8 (50·0%) anti‐HLA‐B and 4 of 6 (66·6%) anti‐HLA class II antibodies have been detected in donors associated with TRALI cases in the literature. Conclusion Platelet apheresis donors without history of immunization have anti‐leucocyte antibodies that potentially can cause TRALI. In our opinion, this cohort should be included in screening strategies for TRALI prevention. As references and consensus cut‐offs have not yet been established, it is premature to use microbead assays as standard for donor screening.