These clinical practice guidelines, however, have based their recommendations on data from published reports on series of patients for whom red cell transfusions were withheld (for instance Jehovah’s witnesses), and observational studies, rather than on the results of clinical trials. However, since then many randomized studies were published comparing a liberal to a restrictive transfusion trigger.
A systematic review from Carson and coworkers (Carson, Carless, Hebert, Cochrane Database Syst. Rev. 2012) showed that restrictive transfusion strategies reduced the risk of receiving a RBC transfusion by 39% (RR 0.61, 95% CI 0.52 to 0.72). This equates to an average absolute risk reduction (ARR) of 34% (95% CI 24% to 45%). The volume of RBCs transfused was reduced on average by 1.19 units (95% CI 0.53 to 1.85 units). However, heterogeneity between trials was statistically significant (P<0.00001; I(2)>93%) for these outcomes. Restrictive transfusion strategies were associated with a statistically significant reduction in hospital mortality (RR 0.77, 95% CI 0.62-0.95) but not 30 day mortality (RR 0.85, 95% CI 0.70 to 1.03). The use of restrictive transfusion strategies did not reduce functional recovery, hospital or intensive care length of stay. The majority of randomized patients were included in good quality trials, but some items of methodological quality were unclear. There are no trials in patients with acute coronary syndrome. The authors concluded that the existing evidence supports the use of restrictive transfusion triggers in the majority of patients, included patients with a cardiovascular history (Carson et al, Transfusion 2006).
A more recent meta-analysis including 31 randomized trials (n=9813) again concluded that a restrictive transfusion trigger reduced transfusion rate (RR 0,54, 95% CI 0,47 to 0,63) and the number of transfused RBC units (1,43 units, 95% CI 0,86 to 2,01 units) without any difference in overall mortality and overall morbidity (Holst et al. BMJ 2015).
Another systematic review focussed on the effect of transfusion thresholds on postoperative infection rate and concluded that using restrictive transfusion thresholds lowered infection risk (Holst et al. New Eng J Med 2014).
However, additional evidence regarding a randomized trial among cardiac surgery patients found no differences in infection rate and other postoperative complications between the liberal and restrictive groups, however more patients died after 90 days in the restrictive group (OR 1.64 95% CI 1.00 to 2.67; p=0.045) (Murphy et al. New Eng J Med 2015).
A study of interest was published by Villanueva and coworkers. These authors concluded that a restrictive transfusion strategy significantly improved outcome in patients with acute upper gastrointestinal bleeding (Villanueva et al. New Eng J Med 2013).