Ten studies (one randomised trial and nine observational studies) were included in the review (203,757 patients; reporting differences were noted between tables and text). The authors stated that most studies were considered to have intermediate risk of bias. Follow-up ranged from one month to 12 months, where reported. There was no evidence of publication bias.
Meta-analyses showed that blood transfusion/liberal blood transfusion increased all-cause mortality compared to no blood transfusion/restricted blood transfusion in anaemic patients with myocardial infarction (RR 2.91, 95% CI 2.46 to 3.44; Ι²=92%; NNH=8; 10 studies). Similar results were found when using adjusted mortality instead of the actual number of events (HR 2.25, 95% CI 1.68 to 3.02; Ι²=98%; nine studies). Blood transfusion/liberal blood transfusion was also associated with a higher risk of subsequent myocardial infarction (RR 2.04, 95% CI 1.06 to 3.93; Ι²=98; seven studies).
Subgroups of patients with ST-segment elevation myocardial infarction and patients with haematocrit of less than 30% showed no significant difference in mortality between blood transfusion and comparator.
Meta-regression showed that blood transfusion was associated with higher mortality after adjustment of different variables. Sensitivity analysis confirmed that no single study was the source of heterogeneity. Study sequential analysis of observational studies on all-cause mortality suggested firm evidence for a 20% relative risk increase with blood transfusion or a liberal blood transfusion strategy compared with no blood transfusion or a restricted blood transfusion strategy.