A process used to filter and remove white blood cells from whole blood before transfusion. Leukocytes are removed from blood because they provide no benefit to the recipient but may carry bacteria and viruses to the recipient. Patients who receive blood that has not been leuko-reduced may have adverse effects, including fever with chills; alloimmunization, an immune system reaction that can compromise a later transfusion; and the transmission of viruses, including cytomegalovirus, which can be dangerous for low-birth weight infants and to immunosuppressed patients.