Pneumonia as a complication of blood product transfusion in the critically ill: transfusion-related immunomodulation (TRIM).

BACKGROUND: An increased risk of postoperative infection (including pneumonia) attributable to the receipt of allogeneic blood transfusion has been investigated as a possible manifestation of transfusion-related immunomodulation (TRIM) in 16 randomized controlled trials (RCTs) and approximately 40 observational studies.

OBJECTIVES: This review categorizes RCTs and observational studies with regard to the inference that they permit about possible mediators of TRIM-allogeneic white cells (WBCs), WBC-derived soluble mediators, and/or allogeneic plasma-and examines whether the totality of the clinical evidence supports an association between allogeneic blood transfusion and postoperative infection.

RESULTS: When all available studies are considered together in meta-analyses, three types of studies show no increased risk of postoperative infection in association with allogeneic blood transfusion: a) RCTs comparing recipients of buffy-coat-reduced and prestorage-filtered, WBC-reduced allogeneic red cells; b) RCTs comparing recipients of allogeneic and autologous blood; and c) observational studies comparing patients transfused before and after implementation of WBC reduction. RCTs comparing recipients of nonbuffy-coat-reduced and WBC-reduced red blood cells may point to a TRIM effect, but they cannot yet be subjected to formal meta-analysis.

CONCLUSIONS: No overwhelming clinical evidence has been presented to establish the existence of a TRIM effect that relates allogeneic blood transfusion to postoperative infection.