For patients with acute heart problems, a blood transfusion--an increasingly common procedure--can double the risk of death and triple the risk of another heart attack within a month, according to a study in the Journal of the American Medical Association. Doctors at Duke Clinical Research Institute analyzed data from three big trials involving more than 24,000 patients, 10% of whom had had transfusions during their first 30 days in the hospital. Researchers speculate that transfused blood may lack nitric oxide--essential for delivering oxygen to tissues--and cause harmful inflammation. Transfusions can't be halted, says the study's lead author, but cardiologists can be...

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