Clinical Significance of Red Cell Age in Transfusions
Statement Before the Advisory Committee on Blood Safety and Availability
May 30, 2008
Presented by Darrell Triulzi, MD
AABB, the American Red Cross and America’s Blood Centers (ABC) thank the advisory committee for considering the important issues surrounding the clinical significance of red cell age in transfusions. As the committee will hear more about today, in recent months there have been some interesting studies regarding the repercussions red cell age may have on patient care. Our organizations believe that additional, prospective randomized clinical trials (RCTs) are needed to provide sufficient evidence to determine whether “older” red blood cells do in fact impact outcomes and, if so, what steps need to be taken to improve patient care.
The trials on red cell age have not been conclusive. Recently, there have been four retrospective studies (1-4) and two small prospective randomized trials (5,6) regarding the age of blood. In the retrospective studies of age of blood in cardiac surgery, two showed worse outcomes (3,4) in those who received older units and two found no effect of the age of the units on outcomes (1,2). Neither of the two small prospective trials found a worse outcome in those receiving older units (5,6). In fact, in a 66 patient pilot RCT study, Hebert et al (5) reported a worse outcome in recipients of fresher units in their ICU population although this was not statistically different due to the small sample size.
It should be noted that there are inherent limitations in any retrospective study, including the study by Koch et al (4) published recently in the NEJM. There are clear differences between the groups, such as a significantly higher incidence of left ventricular dysfunction and use of leukoreduced components in the older blood recipients. It should also be noted that in any retrospective study, including this one, there are unavoidable limitations in the ability to account for known or unknown confounders that could affect outcome. Retrospective observational studies are hypothesis generating and, in general, should not be used to establish major changes in practice. Given that the retrospective studies are divided and that the prospective randomized clinical trials do not show a benefit from “younger” units, we believe that a change in clinical practice is not justified at this time.
Instead, randomized clinical trials, such as those being designed by the National Institutes of Health, should be supported and pursued. Our organizations commend NIH for sponsoring this critical research, including a randomized trial of the age of blood that will potentially include about 1600 cardiac surgery patients. We are also pleased to hear that the Canadian health authority is supporting a randomized clinical trial on the age of blood in ICU patients. This research is clearly needed to ensure we are providing patients with the best possible transfusion medicine.
As with all transfusion medicine policies, attention must be paid to the impact of such policies on the available blood supply, since blood availability itself is a safety concern. Changing clinical practice to transfuse only younger units could have significant repercussions on blood inventory and outdating of red cells. As this committee is well aware, many areas across the country already are battling to keep sufficient inventories on hand and would struggle considerably if forced to outdate red blood cells at an earlier date.
Unfortunately, it is difficult to fully predict the possible effect of any policy change on blood supplies because there are no reliable national data regarding the average age of red blood cells transfused in hospitals. Hospital practices and available inventories vary considerably among individual facilities. Our organizations encourage the collection of relevant national data regarding age of RBCs transfused so that we can better understand this complex issue.
AABB, the American Red Cross and ABC caution that clinical practice should not be changed absent improved data regarding RBC supplies and the completion of randomized clinical trials that provide sufficient data to warrant changes. Policies and clinical practice must continue to be driven by our shared goal of providing patients with safe, available blood transfusions.
1. van de Watering L et al. Effects of storage time of red blood cell transfusions on the prognosis of CABG patients. Transfusion 2006;46:1712-18.
2. Vamvakas EC et al. Length of storage of transfused red cells and postoperative morbidity in patients undergoing CABG surgery. Transfusion 2000;40:101-9.
3. Basran S et al. The association between duration of storage of transfused red blood cells and morbidity and mortality after preoperative cardiac surgery. Anesth Analg 2006;103:15-20.
4. Koch CG et al. Duration of red-cell storage and complications after cardiac surgery. N Eng J Med 2008;358:1229-39
5.Hebert PC et al. A pilot trial evaluating the clinical effects of prolonged storage of red cells. Anesthe Anlg 2005;100:1433-8.
6. Walsh TS, et al. Does the storage time of transfused red blood cells influence regional or global indexes of tissue oxygenation in anemic critically ill patients? Crit Care Med 2004:32:364-71.