Prophylactic transfusions usually reserved for platelet count <10,000/µL (<20,000/µL in acute leukemia). One unit elevates the count by about 10,000/µL if no platelet antibodies are present as a result of prior transfusions. Efficacy assessed by 1- and 24-h posttransfusion platelet counts. HLA-matched single-donor platelets may be required in pts with platelet alloantibodies.