Background: Prophylactic platelet transfusions are usually administered to patients receiving myelotoxic chemotherapy when their platelet count falls below 20,000 per cubic millimeter. Some observations suggest that lower platelet counts be appropriate in patients in stable condition, but the safety of lower thresholds in uncertain. Methods: We evaluated 255 adolescents and adults (age, 16 to 70 years) with newly diagnosed acute myeloid leukemia (but not acute promyelocytic leukemia), who were treated in 21 centers. One hundred thirty-five patients were randomly assigned to receive a transfusion when their platelet count fell below 10,000 per cubic millimeter (or 10,000 to 20,000 per cubic millimeter in those with a temperature above 38°C, with active bleeding, or a need for invasive procedures), and 120 patients were assigned to receive a transfusion when their platelet count was less than 20,000 per cubic millimeter. Results: Patients in the group with a threshold of 10,000 platelets per cubic millimeter received 21.5 percent fewer platelet transfusions than the patients in the group with a threshold of 20,000 platelets per cubic millimeter (P = 0.001). The numbers of red-cell units transfused were not significantly different between groups. Major bleeding (defined as any bleeding more than petechiae or mucosal or retinal bleeding) occurred in 21.5 and 20 percent of patients, respectively (P = 0.41), and on 3.1 and 2.0 percent of the days of hospitalization. One episode of fatal cerebral hemorrhage occurred in the group with a threshold of 10,000 platelets per cubic millimeter; none occurred in the other group (P = 0.95). Actuarial estimates of survival during induction chemotherapy actuarial estimates of the absence of major bleeding, and the length of hospital stay were not significantly different in the two groups. Conclusions: The risk of major bleeding during induction chemotherapy in adolescents and adults with acute myeloid leukemia (except acute promyelocytic leukemia, which we did not study) was similar with platelet-transfusion thresholds of 20,000 per cubic millimeter and 10,000 per cubic millimeter (or 10,000 to 20,000 per cubic millimeter when body temperature exceeded 38°C, there was active bleeding, or invasive procedures were needed). Use of the lower threshold reduced platelet use by 21.5 percent.
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