Blood transfusion during acute myocardial infarction: association with mortality and variability across hospitals.
Blood transfusion is controversial for anemic patients with acute myocardial infarction (AMI), with some previous studies reporting increased risk of transfusion-associated mortality. The goal of this study was to examine variability in blood transfusions across hospitals and the relationship between blood transfusion and in-hospital mortality in a large, contemporary cohort of consecutive AMI patients. Among 34,937 AMI hospitalizations from 57 centers, patients receiving at least 1 packed red blood cell transfusion were compared with those who were not transfused. Using 45 disease severity, comorbidity, laboratory, and in-hospital treatment variables, we propensity matched patients who did and did not receive a packed red blood cell transfusion. A conditional logistic regression model was used to identify the association between transfusion and in-hospital mortality. A total of 1,778 patients (5.1%) had at least 1 transfusion. In unadjusted analyses, transfusion was associated with higher in-hospital mortality (odds ratio: 2.05 [95% confidence interval: 1.76 to 2.40]). The vast majority of patients (91.1%) with and without transfusion had nonoverlapping propensity scores, reflecting incomparable clinical profiles. Thus, they were excluded from the propensity-matched analyses. After propensity matching those with overlapping scores, blood transfusion was associated with a reduced risk of in-hospital death (odds ratio: 0.73 [95% confidence interval: 0.58 to 0.92]). The majority of patients undergoing blood transfusion in clinical practice cannot be matched with nontransfused patients due to their markedly different clinical profiles. Among comparable patients, blood transfusion was associated with a lower risk of in-hospital mortality. These findings suggest that previous observational reports of increased mortality with transfusion may have been influenced by selection bias, and they highlight the need for randomized trials to establish the role of transfusion during AMI.