Concern over transfusions in myocardial infarction patients

By Eleanor McDermid, Senior medwireNews Reporter

A meta-analysis highlights the consistent observational finding that patients with myocardial infarction (MI) who receive blood transfusions are at high risk for dying.

However, in a commentary accompanying the study in the Archives of Internal Medicine, Jeffrey Carson (University of Medicine and Dentistry of New Jersey, New Brunswick, USA) and Paul Hébert (Ottawa Hospital Research Institute, Ontario, Canada) say they "remained unconvinced" that transfusions themselves harm MI patients.

"As physicians, we believe that profound anemia is life threatening, and as a consequence transfusions in many patients are life saving," they say.

They point out that just one study in the analysis was a randomized controlled trial; the other nine were observational studies.

"All such studies have a near fatal flaw: that is, patients who need blood transfusions are sicker than patients who do not," say Carson and Hébert. This creates confounding by indication, where patients who are likely to meet the endpoint anyway (mortality in this case) are also likely to receive the treatment (transfusion). The researchers themselves caution that "causality could not be inferred."

Carson and Hébert also note that observational studies showing worse outcomes in patients given transfusions appear to contradict randomized, controlled trials showing that a liberal transfusion policy does no more harm than a restrictive policy.

Across the 10 studies, which included 203,665 patients, 18.2% of those given a blood transfusion died, compared with 10.2% of those not given a transfusion. This equated to a weighted absolute risk increase of 12% and a number needed to harm of eight, and did not change on exclusion of the randomized, controlled trial.

The size of the risk increase was less in studies restricted to patients with ST-elevation MI and in patients with a baseline hematocrit level below 30%, say lead researcher Saurav Chatterjee (Brown University and Providence Veterans Affairs Medical Center, Rhode Island, USA) and colleagues.

The associations were independent of variables including follow-up period, history of bleeding, baseline creatinine level, hemoglobin level, and acute treatments given.

"As physicians we should not use the results of this review to justify or limit the use of red blood cells," say Carson and Hébert.

They add: "Given that real risks and potential benefits exist as to how we choose to use the valuable resource of blood transfusion, we believe that high-quality research is long overdue."

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