Transfusion-associated microchimerism in combat casualties

Fresh whole blood (FrWB) is routinely used in the resuscitation of combat casualties in Operation Iraqi Freedom and Operation Enduring Freedom. However, studies have shown high rates (20%-40%) of transfusion-associated microchimerism (TA-MC) in civilian trauma patients receiving allogenic red blood cell (RBC) transfusions. We explored the incidence of TA-MC in combat casualties receiving FrWB compared with patients receiving standard stored RBC transfusions.

Prospective data on TA-MC at >or=14 days posttransfusion were collected on 26 severely injured combat casualties admitted to the National Naval Medical Center between December 2006 and March 2007. Demographic variables included age, sex, Injury Severity Score, and transfusion history. Data are expressed as mean +/- SD.

The mean age of the study cohort was 24 +/- 7; mean Injury Severity Score was 17 +/- 12. All were men and suffered penetrating injury. Average hospital length of stay was 46 +/- 35 days. TA-MC was present in 45% (10 of 22) patients who were transfused at least 1 unit of blood. The four nontransfused patients all tested negative for TA-MC. Among six patients who received 4 to 43 units of FrWB, five also received RBCs and one aphaeresis platelets. The remaining 16 transfused patients who received RBCs (no FrWB) included seven who also received platelets in theater. The prevalence of TA-MC was 50% (3 of 6) in FrWB patients, 50% in patients given platelets (4 of 8), and 38% (3 of 8) in those given only RBCs as a cellular component (p = 0.61).

Although these preliminary data do not demonstrate a significantly increased rate of TA-MC in FrWB or apheresis platelets recipients compared with RBC recipients, the overall 45% (10 of 22) rate of TA-MC in transfused soldiers warrants further study to ascertain possible clinical consequences such as graft-versus-host or autoimmune disease syndromes.