A debate over the merits of universal leukoreduction (cellular components with <5 x 106 leukocytes) has focused on several potentially important clinical effects, including transfusion-related alloimmunization to platelets (TRAP), febrile-associated transfusion reactions (FATR), and transfusion-related immunomodulation (TRIM). Both leukoreduced and nonleukoreduced blood components remain Food and Drug Administration (FDA)-approved (22).
The percentages of red cell transfusions remained static in the United States between 1994 and 1999 (17.6 and 20%, respectively), despite commercial promotion of leukocyte-depletion filters during this period (4). For the first 9 mo of 1999, 13% of total red cell transfusions at our hospital were leukoreduced; our own indications for leukoreduction reflect those published previously (Table 3) (23).
FATR occur in only 0.5% of patients receiving red blood cell transfusions, and of these, 18 and 8% of patients experience a second or third FATR, respectively (24). Approximately 18% of all platelet transfusions are associated with FATR (24), although the prevalence of platelet-associated FATR can be as high as 30% in frequently transfused populations, such as patients with cancer. Reactions characterized as severe occur in only 2% of platelet transfusions (25), and bedside leukofiltration has not reduced the overall prevalence of FATR (26). Bedside leukoreduction filters can cause significant hypotensive events by activating the bradykinin/kininogen systems, particularly in patients taking angiotensin-converting enzyme (ACE) inhibitors (22). Universal prestorage leukoreduction for red blood cell transfusion has not been shown to change the incidence of transfusion reactions (27) or other clinical outcomes such as in-hospital mortality, duration of hospitalization after transfusion, and total hospital costs (28).
TRAP was studied in a multicenter trial of patients newly diagnosed with leukemia (25). The study found that clinical platelet refractoriness associated with human leukocyte antigen (HLA) seropositivity was reduced from 13% in patients who received transfusions of unprocessed platelet concentrates compared with 3-5% in patients who received leukoreduced apheresis platelets, leukoreduced platelet concentrates, or psoralen/UV-B treated platelets. Although this difference is statistically significant, no clinically impor-
Indications for Leukocyte Reduced Blood Components
Prevention of recurrent nonhemolytic febrile transfusion reactions to red blood cell transfusions Prevention or delay of alloimmunization to leukocyte antigens in selected patients who are candidates for transplantation or transfusion on a long-term basis Indications under review
Prevention of the platelet-refractory state caused by alloimmunization Prevention of recurrent febrile reactions during platelet transfusions Prevention of cytomegalovirus transmission by cellular blood components Not indicated for
Prevention of transfusion-associated graft-versus-host disease
Prevention of transfusion-related acute lung injury due to the passive administration of antileukocyte antibody Patients who are expected to have only limited transfusion exposure Acellular blood components (for example, fresh frozen plasma, cryoprecipitate)
tant differences were found between the patient cohorts in prevalence of transfusion reactions, hemorrhagic events, length of hospital stay, number of platelet transfusions, number of red blood cell transfusions, or mortality.
TRIM was cited as clinically important in patients undergoing renal transplantation and in women who have had multiple miscarriages (29). A multicenter, controlled study found no evidence of such an effect, however, and the authors recommended against allogeneic mononuclear infusions as a treatment for unexplained, recurrent miscarriage
(30). Similarly, patients who received transfusions before renal transplantation had superior 1-yr renal allograft survival compared with patients who did not receive transfusions
(31). When data from patients who did not receive transfusions before surgery were analyzed for blood transfused at the time of transplantation surgery, 1-yr renal allograft survival was not effected. Only a few prospective studies have been done to clarify the potential immunomodulatory effects of allogeneic transfusion in other settings (32). Indications for leukoreduction published in a review in 1992 (21) are listed in Table 3; these guidelines continue to be applicable since the completion of a controlled, prospective clinical trial (28) that found no benefit from universal leukoreduction (22).
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