Death rates after heart surgery are five times higher for patients who are given blood that has been stored for more than 31 days than for those given blood stored for 19 days or less. If the finding is confirmed by larger studies, it could suggest that high-risk patients should be given fresher blood, which may be better able to deliver oxygen.
Donated blood doesn't last forever as red blood cells run down metabolically over time. In the 1980s, however, new preservatives doubled the original shelf life of donated blood to an apparent 42 days--a point at which 75% of red blood cells survive in the body after 24 hours. Still, Elliott Bennett-Guerrero, who directs perioperative clinical research at the Duke University Research Institute in Durham, North Carolina, realized that no large randomized study had tested for possible adverse effects of such old blood.
So Bennett-Guerrero and his colleagues checked the health records of 321 patients who had undergone repeat cardiac surgery. They selected patients who had faced a high risk of death, then corrected for factors such as age and number of transfusions received, both of which are independent indicators of high mortality. Less than 5% of patients who received blood that had been stored between one and 19 days died while in the hospital, but the death rate was about five times higher for those whose blood transfusions had been stored 31 to 42 days. For every extra day that blood was stored, patients had an 8.5% increased chance of in-hospital death. In addition, those who received the oldest blood stayed, on average, twice as long in the intensive care unit compared to those who received the newest blood. Receiving older blood also increased the likelihood of renal failure. The team reports its results in the 22 June issue of Anesthesia and Analgesia.
The authors suspect that these problems may be caused by changes in blood cells that occur during storage. Over time, red blood cells become stiffer, so they take longer to travel through capillaries and do not unload oxygen as effectively. "What's unclear is whether these changes are interfering with the blood's ability to deliver oxygen," says Bennett-Guerrero.
Herbert Meiselman, a physiologist at the University of Southern California, cautions against premature interpretation of the data. While interesting, he notes that the study does not fully take into account all of the confounding factors, such as the positive correlation between the total amount of blood received and the amount of old blood received.
However, Bennett-Guerrero suspects his group's results may have implications for how blood is chosen for transfusions in the future. Because of high demand, it won't be possible to ensure that all patients receive fresh blood. Rather, he says, "we can avoid giving old blood to high-risk patients." For most patients, however, the age of blood may be a nonissue. "If somebody just gets one unit of blood, our hunch is that it probably doesn't matter so much whether it's old or young," says Bennett-Guerrero.
Editor's note: A reader has alerted us that this paper was retracted in the June 2009 issue of Anesthesia and Analgesia at the authors' request, because of concerns that the article's analysis was erroneous. However, a second group has replicated the findings and published them 20 March 2008 in The New England Journal of Medicine—although some still consider the conclusions about older blood to be controversial.