Rephrasing the Question of Whether Blood Transfusion Increases Risk of Adverse Outcomes after Cardiac Surgery

Some studies^1,2  suggest a dose-dependent association of erythrocyte transfusion with postoperative morbidity, hospital stay, and early and late mortalities.^1,2  However, other studies^3,4  suggest that benefits of erythrocyte transfusion outweigh the risks. Recently, in a meta-analysis, using a prespecified context-specific approach and stratifying patients by characteristics and clinical settings, Hovaguimian and Myles.⁵  demonstrated that restrictive transfusion strategies were associated with an increased risk of complications in high-risk patients with major surgery. Although the evidence is robust, a limitation should be noticed. Studies^3–5  usually dichotomize patients based on restrictive or liberal trigger, but hemoglobin levels within each of these groups can vary widely. As a result, hemoglobin concentration may be higher in some patients in the restrictive group than in the liberal group. Therefore, studies to stratify patients based on actual hemoglobin levels are needed. It would be nice if Hovaguimian and Myles.⁵  could provide the criteria for categorizing the restrictive and liberal groups, and if their associated hematocrits in a supplemental table were added to their article. To nullify its interference on the outcome, blood transfusion should be used as a confounding factor in analyzing the effect of actual hemoglobin levels on outcome. To be robust, such subgroup analyses require adequate statistical power, so future studies should be large and preferably involving multiple centers. Such studies would be an important step toward personalized blood transfusion. The meta-analysis by Hovaguimian and Myles.⁵  has made important progress toward this goal.

The authors declare no competing interests.