Measuring bleeding as an outcome in clinical trials of prophylactic platelet transfusions.

A 12-year-old girl with acute myeloid leukemia has completed her third cycle of chemotherapy and is in the hospital awaiting count recovery. Her platelet count today is 15 000 and, based on your institution's protocol, she should receive a prophylactic platelet transfusion. She has a history of allergic reactions to platelet transfusions and currently has no bleeding symptoms. The patient's mother questions the necessity of today's transfusion and asks what her daughter's risk of bleeding would be if the count is allowed to decrease lower before transfusing. You perform a literature search regarding the risk of bleeding with differing regimens for prophylactic platelet transfusions.