Evidence‐based transfusion: young versus old blood as a case study

Abstract

Background Evidence‐based medicine incorporates critical appraisal of the literature, individual clinical expertise, patient values, clinical circumstances and societies’ expectations into medical decision‐making. This approach is increasingly utilized to formulate individual transfusion decisions and to set national transfusion policies.Aims To describe the process of evidence‐based decision‐making and its application to transfusion medicine through the analysis of a test case.Methods Critical appraisal of the literature and evidence‐based medicine techniques are described and applied to the issue of the duration of red cell storage and the incidence of complications after transfusion, as raised by the report of Koch et al. (N Engl J Med 358:12, 1229–39). This report compared the outcomes of patients transfused with blood after ≤ 14 or > 14 days of storage during and after cardiac surgery.Results The methods and logic of literature appraisal and evidence‐based medicine are reviewed, and applied to the paper by Koch et al (N Engl J Med 358:12, 1229–39). This report describes a case‐controlled, retrospective observational study with Level 3‐4 evidence to support the use of younger blood (≤14 days old) in cardiac surgery patients. Issues are raised concerning the equivalence of the prestudy prognosis of the test and control groups and the use of non‐risk adjusted statistics in comparing data. After risk adjustment, the association of an older blood transfusion with a poorly defined composite index of adverse outcomes has only marginal significance (OR: 1·16, 95% CI: 1·01–1·33). Reports of systematic review of the literature reveals 19 publications: 14 studies are retrospective observational studies and many suggest an association of older blood with various adverse outcomes. Five prospective studies fail to show an adverse relationship, however, these are small and underpowered. Society values emphasize the availability of blood products, which at this time requires inventory management practices that prevent the transfusion of blood < 14 days storage on a routine basis for all patients.Conclusions Evidence‐based decision‐making provides a formal process to evaluate the information supporting individual clinical and national policy decisions in transfusion medicine. Application to the specific problem of whether to limit the use of older blood suggests that the level of available evidence does not yet justify changing clinical practice. Adequately powered randomized controlled trials are necessary to determine the relative safety of older blood compared with younger blood in transfusion practice.