Transfusion strategy trials excluding patients transfused outside the trial study period are more likely to report a trend favoring restrictive strategies: a meta-analysis.

Though not statistically significant, there was a consistent difference in trends between RCTs administering significant numbers of transfusion outside the trial study period compared to those that did not. The implications of our results may extend to RCTs in other settings that ignore if and how frequently an investigated therapy is administered outside the trial window.