The indications for red blood cell transfusion are controversial. There is no debate that patients with very low hemoglobin concentrations (< 6 g/dL) should be transfused. However, it is less clear if transfusion is indicated when the hemoglobin concentration is between 6-10 g/dL. A recent cohort study by Glance in 10,000 patients undergoing general, vascular and orthopedic surgery found 29% increase mortality in patients receiving transfusion during the intraoperative time period . An important limitation of this study is that the hemoglobin concentration at the time of transfusion was unknown. This problem was partially overcome by an even larger study (n = 18,646) which found that when the results were stratified by preoperative hematocrit patients with a hematocrit less than 24% had 40% reduced mortality if transfused . This compares to the overall increased odds of death in patients transfused of 1.37 (95% confidence interval, 1.27 to 1.48). In the accompanying editorial, Spahn et al. argue that there is adequate evidence to change transfusion practice even if most of the data comes from observational studies . I agree that the weight of the evidence (including randomized clinical trials  and observational data) supports a restrictive transfusion approach. However, the research needed to define the optimal hemoglobin concentration for transfusion awaits further clinical trials.
– Jeffrey L. Carson
1. Glance LG, Dick AW, Mukamel DB, et al. Association between intraoperative blood transfusion and mortality and morbidity in patients undergoing noncardiac surgery. Anesthesiology 2011;114:283-92.
2. Wu WC, Smith TS, Henderson WG, et al. Operative blood loss, blood transfusion, and 30-day mortality in older patients after major noncardiac surgery. Ann Surg 2010;252:11-7.
3. Spahn DR, Shander A, Hofmann A, Berman MF. More on transfusion and adverse outcome: it’s time to change. Anesthesiology 2011;114:234-6.
4. Carless PA, Henry DA, Carson JL, Hebert PP, McClelland B, Ker K. Transfusion thresholds and other strategies for guiding allogeneic red blood cell transfusion. Cochrane Database Syst Rev 2010:CD002042.