While restrictive transfusion thresholds are beneficial for most patients and reduce blood use by 50%, but transfusion guidelines state there are insufficient data to provide recommendations for patients with acute myocardial infarctions (MI). Only three small randomized clinical trials with a total of 820 patients with MI have compared restrictive vs. liberal transfusion thresholds, and the results have been inconsistent. The Myocardial Ischemic and Transfusion (MINT) trial, just published in the NEJM, enrolled 3506 patients with MI (mean age, 72 years; 45% female) at 144 sites in the U.S., Canada, France, Brazil, New Zealand and Australia. Patients were randomized 1:1 to receive RBCs based on either restrictive (Hb less than 7 or 8 g/dL) or liberal (Hb less than 10 g/dL) transfusion thresholds. During the study, the mean number of RBC units transfused was 0.7 in the restrictive arm compared to 2.5 in the liberal arm, and mean hemoglobin values were 1.6 g/dL lower in the restrictive arm three days after randomization. The risk of 30-day mortality or recurrent MI was slightly greater in the restrictive transfusion group (16.9%) as compared to the liberal transfusion threshold group (14.5%), but this difference was not statistically significant (RR 1.15, 95% C.I., 0.99 to 1.34, p=0.07). Furthermore, point estimates for all causes of death, cardiac death, recurrent MI, and readmission to the hospital all suggest a slight benefit for a liberal transfusion threshold for patients with MI. While the results are not statistically significant, the risk of MI or death substantially outweighs the generally mild or extremely rare transfusion related adverse events. Thus, a liberal transfusion strategy data may be best for patients with an MI. Further analysis of different cardiovascular subgroups is needed.
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