Comparison 6. Blood transfusions.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
6.1 Participants exposed to blood transfusion (all trials)	42	20057	Risk Ratio (M‐H, Random, 95% CI)	0.59 [0.53, 0.66]
6.2 Participants exposed to blood transfusion by clinical specialties	41	19977	Risk Ratio (M‐H, Random, 95% CI)	0.59 [0.53, 0.66]
6.2.1 Cardiac surgery	7	8598	Risk Ratio (M‐H, Random, 95% CI)	0.69 [0.66, 0.73]
6.2.2 Orthopaedic surgery	11	3969	Risk Ratio (M‐H, Random, 95% CI)	0.49 [0.38, 0.65]
6.2.3 Vascular surgery	2	157	Risk Ratio (M‐H, Random, 95% CI)	0.79 [0.57, 1.08]
6.2.4 Acute blood loss/trauma	5	2416	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.23, 0.67]
6.2.5 Critical care	9	3529	Risk Ratio (M‐H, Random, 95% CI)	0.66 [0.57, 0.77]
6.2.6 Acute myocardial infarction	3	821	Risk Ratio (M‐H, Random, 95% CI)	0.38 [0.28, 0.53]
6.2.7 Haematological malignancies	4	487	Risk Ratio (M‐H, Random, 95% CI)	0.88 [0.61, 1.26]
6.3 Participants exposed to blood transfusion (by transfusion threshold)	33		Risk Ratio (M‐H, Random, 95% CI)	Subtotals only
6.3.1 Difference between liberal and restrictive haemoglobin thresholds ≥ 2.0 g/dL	27	15072	Risk Ratio (M‐H, Random, 95% CI)	0.57 [0.50, 0.64]
6.3.2 Difference between liberal and restrictive haemoglobin thresholds < 2.0 g/dL	6	2966	Risk Ratio (M‐H, Random, 95% CI)	0.80 [0.63, 1.02]
6.4 Participants exposed to blood transfusion by transfusion threshold	36	17954	Risk Ratio (M‐H, Random, 95% CI)	0.57 [0.51, 0.64]
6.4.1 Restrictive 7.0 g/dL to 7.5 g/dL	17	11919	Risk Ratio (M‐H, Random, 95% CI)	0.55 [0.48, 0.64]
6.4.2 Restrictive < 8.0 g/dL to 9.0 g/dL	19	6035	Risk Ratio (M‐H, Random, 95% CI)	0.59 [0.48, 0.72]
6.5 Units of blood transfused	17	6253	Mean Difference (IV, Random, 95% CI)	‐1.21 [‐1.67, ‐0.75]