Comparison 6. Blood transfusions.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Participants exposed to blood transfusion (all studies)	31	12587	Risk Ratio (M‐H, Random, 95% CI)	0.57 [0.49, 0.65]
2 Participants exposed to blood transfusion by clinical specialties	31	12587	Risk Ratio (M‐H, Random, 95% CI)	0.57 [0.49, 0.65]
2.1 Cardiac surgery	5	3021	Risk Ratio (M‐H, Random, 95% CI)	0.67 [0.64, 0.70]
2.2 Orthopaedic surgery	10	3907	Risk Ratio (M‐H, Random, 95% CI)	0.50 [0.38, 0.67]
2.3 Vascular	1	99	Risk Ratio (M‐H, Random, 95% CI)	0.91 [0.77, 1.08]
2.4 Acute blood loss/trauma	5	2416	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.23, 0.67]
2.5 Critical care	6	2840	Risk Ratio (M‐H, Random, 95% CI)	0.63 [0.55, 0.72]
2.6 Acute myocardial infarction	2	155	Risk Ratio (M‐H, Random, 95% CI)	0.40 [0.19, 0.82]
2.7 Haematological malignancies	2	149	Risk Ratio (M‐H, Random, 95% CI)	1.00 [0.95, 1.05]
3 Participants exposed to blood transfusion (by transfusion threshold)	26		Risk Ratio (M‐H, Random, 95% CI)	Subtotals only
3.1 Difference between liberal and restrictive haemoglobin thresholds ≥ 2 g/dL	19	7683	Risk Ratio (M‐H, Random, 95% CI)	0.56 [0.48, 0.65]
3.2 Difference between liberal and restrictive haemoglobin thresholds < 2 g/dL	7	3903	Risk Ratio (M‐H, Random, 95% CI)	0.79 [0.63, 0.98]
4 Participants exposed to blood transfusion by transfusion threshold	31	12587	Risk Ratio (M‐H, Random, 95% CI)	0.57 [0.49, 0.65]
4.1 Restrictive < 7 g/dL	12	6453	Risk Ratio (M‐H, Random, 95% CI)	0.58 [0.47, 0.72]
4.2 Restrictive < 8 g/dL to 9 g/dL	19	6134	Risk Ratio (M‐H, Random, 95% CI)	0.55 [0.46, 0.67]
5 Units of blood transfused	12	4674	Mean Difference (IV, Random, 95% CI)	‐1.30 [‐1.85, ‐0.75]