yasser sakr and konrad reinhart we read with interest the comment by mller and juffermans . in our study , we did not attribute the possible beneficial effects of red cell transfusion only to leukoreduction . the different case mix in our study and the possible change in practice and quality of care could have been other factors explaining our results . in addition , intensivists are now more aware of the meaning of various parameters that reflect tissue oxygenation and microvascular perfusion . these parameters are increasingly used in the icu in addition to clinical evaluation to establish indications for blood transfusion . mller and juffermans also misinterpreted our data somewhat , by assuming that the indication for blood transfusion was mostly active bleeding . the fact that 76% of patients were referred from the operating / recovery room is simply because our icu is a surgical icu , and the median icu stay in transfused patients was 4 days and not 1 day . around 58% of our patients received only 1 or 2 units of blood and the number of transfused units was not associated with a higher risk of death in the multivariate analysis . our previous observation from the sepsis occurrence in acutely ill patients study in a mixed icu population also does not support the active bleeding hypothesis as a single important player . generalizing the evidence derived from the literature without taking into consideration the specific case mix may not be justified . in surgical icu patients , results from a large cohort like ours are hypothesis generating and may guide clinical practice pending the results of randomized control trials .
the observation of sakr and colleagues that transfusion may be beneficial in certain subgroups of intensive care unit ( icu ) patients [ 1 ] is interesting , since large observational studies demonstrate that transfusion is independently associated with an increased risk of death [ 2 ] . 
 also , a systematic review showed that the benefits of transfusion in the icu do not outweigh the risks [ 3 ] . 
 sakr and colleagues ascribe their discrepant results to the fact that transfused blood was leukoreduced . of the 17 
 randomized controlled trials on the association of nonleukoreduced blood with mortality , however , a benefit of leukoreduction was found only in cardiac surgery patients [ 4 ] . 
 a meta - analysis confirmed that available evidence does not justify universal leukoreduction [ 5].given the increased risk of nosocomial infection , multiple organ failure and acute respiratory distress syndrome , an explanation of a beneficial effect from transfusion in anemic critically ill patients is tempting . 
 we propose that the results of this study may be related to the indication of transfusion , this being active bleeding and not correction of anemia associated with critical illness . 
 hereby , transfusion may have prevented adverse events due to postoperative bleeding , explaining the survival benefit . 
 the fact that 76% of patients were referred from the operating / recovery room and that the median length of icu stay was only 1 day may support this hypothesis . based on numerous reports on the association of transfusion with adverse outcome , a liberal transfusion strategy in critically ill anemic patients in the absence of acute bleeding should not be advocated .