Randomized controlled trials have shown a reduction in platelet alloimmunization and refractoriness in patients with acute leukemia (AL) with the use of poststorage leukoreduction of blood products. Universal prestorage leukoreduction (ULR) of red cell and platelet products has been performed in Canada since August 1999. We conducted a retrospective analysis of 13 902 platelet transfusions in 617 patients undergoing chemotherapy (CT) for AL or stem cell transplantation (SCT) before (n ‫؍‬ 315) and after (n ‫؍‬ 302) the introduction of ULR. Alloimmunization was significantly reduced (19% to 7%, P < .001) in the post-ULR group. Alloimmune platelet refractoriness was similarly reduced (14% to 4%, P < .001). Fewer patients in the post-ULR group received HLA-matched platelets (14% vs 5%, P < .001). Alloimmunization and alloimmune refractoriness in the 318 patients who were previously pregnant and/or transfused were also reduced after ULR (P ‫؍‬ .023 and P ‫؍‬ .005, respectively). In a Cox regression model, the 3 independent factors that predicted for alloimmune refractoriness were nonleukoreduced blood

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Alloimmunization and platelet refractoriness occur in pediatric oncology and bone marrow transplant patients, but the incidence--particularly in children with acute myelogenous leukemia--appears to be low. The detection of LCTAbs predicts a poor response to random-donor platelet transfusion, but most such patients show improved CCIs with HLA-matched platelets. Routine use of white cell-reduction filters has thus far failed to eliminate alloimmunization in children requiring prolonged blood component support.