After an acute myocardial infarction (AMI), blood transfusion to counter anemia associated with antithrombotic medications may do more harm than good, according to a meta-analysis published online December 24, 2012, ahead of print in the Archives of Internal Medicine.

Investigators led by Saurav Chatterjee, MD, of Brown University (Providence, RI), analyzed 10 studies involving 203,665 AMI patients that compared blood transfusion strategies for anemia and outcomes. The studies, conducted between 2001 and 2011, included 9 observational and 1 randomized.

Mortality Increased Almost Threefold 

Blood transfusion compared with no transfusion during MI was associated with increased all-cause mortality (18.2% vs. 10.2%; RR 2.91; 95% CI 2.46-3.44; P < 0.001), with a weighted absolute risk increase of 12% (P < 0.001) and a number needed to harm of 8 (95% CI 6-17). 

Multivariate analysis showed the increased risk remained after adjustment for multiple variables including length of follow-up, history of bleeding, baseline creatinine level, baseline hemoglobin level, nadir of hemoglobin level, and change in hemoglobin level during hospital stay, as well as use of glycoprotein IIb/IIIa inhibitors or thrombolytic or antiplatelet agents. 

However, the mortality risk with blood transfusion was attenuated when analysis was restricted to studies that included patients with STEMI (RR 2.89; 95% CI 0.54-15.58; P = 0.22) or a baseline hematocrit of less than 30% (RR 1.72; 95% CI 0.39-7.63; P = 0.47). 

According to the authors, a sequential analysis taking into account study size suggested evidence for a 20% relative risk increase with blood transfusion or a liberal blood transfusion strategy compared with a strategy of no transfusion or restricted transfusion.

Blood transfusion was also associated with a higher risk for subsequent MI (RR 2.04; 95% CI 1.06-3.93; P = 0.03). 

The latter finding is consistent with studies indicating that blood transfusion has detrimental effects on platelet aggregation, the investigators say, as well as with “recent recommendations by the AABB (formerly American Association of Blood Banks) and in a prior Cochrane review for a restrictive blood transfusion policy in critically ill patients.” 

In addition, the apparent mitigation of the risk of transfusion in STEMI patients and those with a baseline hematocrit of less than 30% suggests a direction for further research in identifying specific subgroups that may gain a net benefit from blood transfusion, they observe. 

Confounding a 'Near Fatal Flaw'? 

In an accompanying editorial, Jeffrey L. Carson MD, of the University of Medicine and Dentistry of New Jersey (New Brunswick, NJ), and Paul C. Hébert, MD, of the Ottawa Hospital Research Institute (Ottawa, Canada), assert that the observational studies underlying the meta-analysis “have a near fatal flaw: that is, patients who need blood transfusions are sicker than those who do not. Those patients are also more likely to have lethal or life-threatening complications.” 

Moreover, they say, because transfusion is life-saving in many patients, the study authors could have been expected to ask “more nuanced, clinically relevant questions” such as “What is a safe hemoglobin transfusion trigger in most patients?” or “Which patients experiencing an [AMI] are at greater risk for transfusions or anemia than others?” 

Due to the many limitations of the study, Drs. Carson and Hébert conclude that clinicians should not use the results to justify or limit the use of red blood cells. “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,” they add. 

 

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Sources:
1. Chatterjee S, Wetterslev J, Sharma A, et al. Association of blood transfusion with increased mortality in myocardial infarction: A meta-analysis and diversity-adjusted study sequential analysis. Arch Intern Med. 2012;Epub ahead of print.

2. Carson JL, Hébert PC. Here we go again—blood transfusion kills patients? Arch Intern Med. 2012;Epub ahead of print.

 

 

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