The indications for transfusion of blood products continue to evolve. The hemoglobin concentration alone is an inadequate indication for red blood cell transfusion but improved clinical guidelines have not yet been defined. The importance of this issue is underscored by evidence that suggests that more liberal use of red blood cell transfusion may possibly harm younger, less severely ill patients in the intensive care unit.8 Similar questions pertain to the indications for platelet concentrates, plasma, and specialized blood products (eg, leukoreduced cellular products, cytomegalovirus seronegative blood, washed red blood cells, fresh blood).
Alloimmunization is a major clinical problem in transfusion medicine, particularly in the setting of patients with multiple transfusions who become refractory to both red blood cells and platelet concentrates. For example, patients with hemoglobinopathies, such as sickle cell disease, rely heavily on transfusions for prevention and treatment of stroke, treatment for acute pulmonary disease, and preparation for surgery.9 Unfortunately, a large percentage of sickle cell disease patients (25%-30%) develop multiple alloantibodies and autoantibody syndromes and become refractory to transfusion. Similarly, patients undergoing stem cell transplantation and aggressive chemotherapy often require frequent and sustained platelet transfusion support. A significant proportion of patients (30%) develop anti-HLA antibodies, resulting in platelet refractoriness.10 A different aspect of alloimmunization pertains to graft-vs-host disease, in which transfused allogeneic T cells react with antigens on host tissues. These allogeneic T cells are transfused via traditional blood components (eg, packed red blood cells and platelet concentrates) or via stem cell products for hematopoietic stem cell transplantation.
There is also a deliberate use of alloimmunity in transfusion medicine, which involves the transfusion of allogeneic T cells to induce a graft vs leukemia/tumor effect for treatment of residual or recurrent tumor.11 In addition, transfusion of viable donor leukocytes may induce ill-defined immunosuppression, referred to as the immunomodulatory effect, leading to tumor recurrence and postoperative infections.12 It has been argued that more research is needed to understand the biology and clinical implications of the immunomodulatory effect before expensive strategies, such as universal leukoreduction of blood products, are instituted.13