Introduction: Patients with severe thrombocytopenia are presumed to be at increased
risk for bleeding, and consequently it has been a standard practice for the past four decades to give
allogeneic platelet transfusions to severely thrombocytopenic patients as supportive care. Platelet
transfusions may be given either prophylactically to reduce the risk of bleeding, in the absence of
clinical hemorrhage (prophylactic transfusions), or to control active bleeding when present (therapeutic
Conclusion: Here we review the structure and function of platelets and discuss the mechanisms of
alloimmunization to platelet transfusion.