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Alloimmunization following platelet transfusion: the absence of a dose-response relationship.

A major concern about the use of prophylactic platelet transfusions is the development of alloimmunization. To determine whether the rate of alloimmunization is related to the number of platelet transfusions, we measured the development of lymphocytotoxic antibody in the first 2 mo of induction therapy in patients with acute nonlymphocytic leukemia. All patients received prophylactic random donor platelets and packed red blood cells during induction. No patient had lymphocytotoxic antibody present at admission. One hundred and six patients received an average of 9.3 platelet transfusions (range 2-34) containing an average of 61 U (range 9-236). The rate of alloimmunization was 38% overall and correlated with refractoriness to platelet transfusions. Ten of 19 patients receiving less than or equal to 4 transfusions became immunized, compared with 30/87 patients receiving less than 4 transfusions. There was no relationship between the number of platelet transfusions given and the rate of severity of alloimmunization, suggesting prophylactic platelets need not be withheld expressly to prevent alloimmunization.