Review of available evidence supporting different transfusion thresholds in different patient groups with anemia.

In patients with anemia, transfusion of red blood cells (RBCs) can save lives and improve quality of life. The choice to transfuse should be cautiously made owing to risks of transfusion, economic costs, and limitations on the blood supply. Until the 1980s, the decision for RBC transfusion was guided by Hb threshold, with the aim of maintaining the patient's blood Hb level over 100 grams per liter. Since then, multiple randomized controlled trials and key systematic reviews have provided evidence-based guidelines as to appropriate transfusion thresholds in a number of clinical settings. Here, we aimed to address the outcome of defining different anemia criteria in specific clinical populations exclusively on the basis of the need for RBC transfusion based on Hb concentration. We focused on the patient populations, where there were the most available data on differing transfusion thresholds, which looked at transfusing to a higher or liberal transfusion threshold in comparison with a lower or restrictive transfusion threshold. These included patients in intensive care with or without septic shock, hip fracture surgery, cardiovascular surgery, and upper gastrointestinal bleeding, the pediatric population, and also those with malaria, by reviewing key randomized controlled trials and systematic reviews. Twenty-four randomized controlled studies and 12 systematic reviews have been included, and these are discussed below.