After the decision has been made to transfuse blood products, the most appropriate product must be chosen. Donated whole blood and other products are modified in several ways that remove varying proportions of nonred cell components. It is important to know the policies of the blood center you are working with.

Packed red blood cells (PRBCs) are the blood product of choice for replacement during surgery, red cell loss, or for transfusion therapy. PRBCs are stored with a preservative solution that enables them to be used 35 to 45 days after collection. The process of removing white blood cells (WBCs) from blood products is referred to as leukoreduction, and is done by highly efficient filters that reduce the number of WBCs by >99.9 %. There are several adverse consequences of transfused WBCs that are reduced by leukoreduction. Febrile nonhemolytic transfusion reactions are mediated by leukocyte-derived cytokines and direct donor cell leukocyte interactions.

In addition, human leukocyte antigen alloimmunization can be induced by human leukocyte antigens expressed on donor leukocytes in recipients who receive multiple transfusions. Allosensitization increases the risk of graft rejection in children who subsequently receive organ or hematopoietic cell transplantation, and increases platelet refractoriness in patients requiring multiple platelet reactions. WBCs can also transmit infectious agents that are harbored in WBCs—most notably cytomegalovirus (CMV). Leukoreduction significantly reduces, but does not completely eliminate these reactions. Many blood centers in the United States have adopted a “universal leukoreduction” policy in which all PRBCs are leukoreduced.