Liberal versus restrictive red blood cell transfusion thresholds in acute acquired brain injury: a systematic review and meta-analysis

OBJECTIVE: To evaluate the effects of liberal transfusion strategy (trigger haemoglobin ≤90-100 g/L) compared with a restrictive strategy (trigger haemoglobin ≤70-80 g/L) on long-term neurological functional outcome in anaemic adult patients with acute acquired brain injury (ABI). DESIGN: Systematic review and study-level meta-analysis of randomised controlled trials (RCTs). DATA SOURCES: MEDLINE, EMBASE, Cochrane from inception to 6 February 2025. STUDY SELECTION: RCTs enrolling patients with acute ABI and anaemia (haemoglobin ≤100 g/L), comparing a liberal vs restrictive transfusion strategy. DATA EXTRACTION AND SYNTHESIS: Two reviewers independently identified eligible studies, extracted data and assessed risk of bias. We performed random-effects meta-analysis of RCTs and applied Grading of Recommendations, Assessment, Development and Evaluation methodology to assess the certainty of evidence. Our primary outcome was an unfavourable neurological functional outcome, using the Glasgow Outcome or modified Rankin scales. RESULTS: Five trials enrolling 2364 patients with acute ABI and anaemia were included in the primary analysis. Liberal transfusion reduces the risk of unfavourable neurological outcome (risk ratio (RR)=0.89, 95% CI 0.84 to 0.95, high certainty). Liberal transfusion may reduce severe disability (RR=0.82, 95% CI 0.66 to 1.02, moderate certainty), and increase good recovery compared with restrictive transfusion (RR=1.29, 95% CI 0.95 to 1.76, low certainty). We found no difference in the risk of most adverse events, including death. Statistical heterogeneity was low (I²=0%-36%) for neurological outcomes. CONCLUSIONS: In adults with acute ABI and anaemia, liberal transfusion reduces the risk of unfavourable outcome (high certainty) and possibly improves the chances of good recovery (low certainty) when compared with restrictive transfusion. PROSPERO REGISTRATION NUMBER: CRD42025628732.