The numbers of platelet transfusions administered in the United States increased dramatically during the 1980s, and has continued to grow as increasingly aggressive medical and surgical treatments have been developed and become more widely available. In particular, the growth of more intensive treatments for hematologic and other malignancies has spurred demands for platelet transfusion support and put pressure on platelet inventories nationwide.
The response to a platelet transfusion is affected by platelet recovery and platelet survival and includes the random loss of platelets in maintaining endothelial integrity. In a normal individual, weighing 70 kg, approximately 4.8 × 1010 platelets per day will be consumed maintaining the endothelium, less than the number of platelets in a single concentrate. However, many clinical conditions can adversely affect platelet recovery and platelet survival in the circulation. Prophylactic platelet transfusion is an important part of supportive care of patients with hypoproliferative thrombocytopenia because of hematologic malignancy and the effects of its treatment with cytotoxic drugs. A morning blood platelet count of less than 10 × 109/L appears to be an appropriate threshold for prophylactic transfusion. Although higher thresholds may be indicated for patients at high risk or who have active bleeding, little or no data support specific platelet count goals and a transfusion plan should be guided by the clinical setting. Larger doses of platelets do not confer additional protection against bleeding in this patient population, although they do result in higher increments and a longer interval until the next platelet transfusion, a potential benefit in the outpatient setting. The platelet count at which an invasive procedure or major surgery can be safely performed is not supported by randomized control studies and practice has been governed by retrospective data and case reports. Most minor invasive procedures and even major surgery can be safely performed at platelet counts of 20 to 50 × 109/L whereas high-risk procedures or severe bleeding may require platelet counts above 100 × 109/L. Patients may become refractory to platelet transfusion and fail to respond for many reasons. Patients alloimmunized to platelets may respond to platelet transfusions from class I human leukocyte antigen (HLA)-matched donors.
Platelets can be collected by apheresis or obtained from whole blood and pooled for transfusion. Both preparations have comparable effectiveness in the prevention of bleeding in patients with hematologic malignancy. Platelets should remain at room temperature and so are approved for only 5 days of storage because of risks of bacterial contamination and may lose viability within days after that. Leukocyte reduction of platelet components, either upon apheresis collection or by filtration, reduces HLA alloimmunization, prevents cytomegalovirus transmission by transfusion, and reduces febrile transfusion reactions. Pathogen reduction of platelets prevents replication of RNA and DNA in contaminating organisms and leukocytes and may prevent alloimmunization and decrease transfusion reactions. Prospective clinical trials are needed to better define indications for platelet transfusion and improve upon the effectiveness of transfusion therapy.