SR and MA (Based on 4 included studies)

Combined total number of transfusion events for patients who received pre-operative IV iron = 334

Combined total number of transfusion events for no treatment = 317

Risk difference (95% CI) = -0.13 (-0.27 to 0.01); P = 0.07; I² = 65%

Risk ratio (95% CI) = 0.57 (0.30 to 1.09); P = 0.09; I² = 64%

SR and MA (Based on 5 included studies)

Combined number of transfusion events for patients who received IV iron therapy = 289

Combined number of transfusion events for control group = 429

Risk ratio (95% CI) = 0.65 (0.48 to 0.88); P = 0.005; I² = 0%

SR and MA

Combined number of transfusion events for patients who received IV iron therapy = 445

Combined number of transfusion events for placebo or standard of care group = 428

Risk ratio (95% CI) = 0.84 (0.71 to 0.99); P = 0.04; I² = 0%

Number of patients receiving blood transfusion (fixed effects model based on 8 studies)

Combined number of transfusion events for patients who received IV iron therapy = 445

Combined number of transfusion events for placebo or standard of care group = 428

Risk ratio (95% CI) = 0.83 (0.70 to 0.98); P = 0.03; I² = 0%

Direct comparison between IV iron and oral iron therapy for number of blood transfusions (random effects model based on 3 studies)

Combined number of transfusion events for patients who received IV iron therapy = 139

Combined number of transfusion events for patients who received oral iron therapy = 144

Risk ratio (95% CI) = 0.88 (0.51 to 1.51); P = 0.63; I² = 37%

SR (1 RCT, Brisbe et al. 2014)

IV iron group = 3/59 (5.1%)

Oral iron group = 2/62 (3.2%)

SR (1 RCT, Khalafallah et al. 2016)

IV iron group = 1/103 (0.1%)

Standard of care group = 5/98 (5.1%)

SR (1 RCT, Kim et al. 2017)

IV iron group = 3/218 (1.4%)

Placebo group = 4/219 (1.8%)

SR (1 RCT, Padmanabhan et al. 2019)

IV iron group = 16/20 (80%)

Oral iron group = 12/20 (60%)

SR (1 RCT, Park et al. 2019)

IV iron group = 2/29 (6.9%)

Placebo group = 4/29 (12.8%)

SR (1 retrospective cohort study, Laso-Morales et al. 2017)

IV iron group = 17%

Control group = 16%

P = NS

Mean amount of blood transfused per patient (unit not specified)

IV iron group = 0.4

Control group = 0.3

P = NS

SR (1 retrospective and prospective cohort study, Calleja et al. 2015)

IV iron group = 9.9%

Control group = 38.7%

P < 0.001

Mean amount of blood transfused per patient (unit not specified)

IV iron group = 0.2

Control group = 0.8

P < 0.001

SR (1 prospective cohort study, Kam et al. 2020)

IV iron group = 1.42%

Control group = 0.55%

P = 0.076

RCT

IV iron group = 1 (5%)

Control group = 3 (15%)

P = 0.605

Number of patients receiving postoperative red blood cell transfusion, n (%)

IV iron group = 1 (5%)

Control group = 4 (20)

P = 0.342

RCT

IV iron group = 6 (46.2%)

Oral iron group = 6 (46.2%)

P = 1.0

Number of patients who received red blood cell transfusion pre-operatively, n (%)

IV iron group = 0

Oral iron group = 3 (23.1%)

P = 0.07

Number of patients who received red blood cell transfusion intra-operatively, n (%)

IV iron group = 6 (46.2%)

Oral iron group = 1 (7.7%)

P = 0.03

Number of patients who received red blood cell transfusion post-operatively, n (%)

IV iron group = 2 (15.4%)

Oral iron group = 4 (30.8%)

P = 0.4

Retrospective cohort study

IV iron group = 55 (45%)

Control group = 19 (40%)

Median number of pre-operative red blood cell transfusions between IV iron group (N = 122) and control group (N = 48), n (%)

IV iron group = 29 (24%)

Control group = 16 (33%)

Median number of the day of surgery red blood cell transfusions between IV iron group (N = 122) and control group (N = 48), n (%)

IV iron group = 13 (11%)

Control group = 2 (4%)

Median number of postoperative day 1 to 30 red blood cell transfusions between IV iron group (N = 122) and control group (N = 48), n (%)

IV iron group = 24 (20%)

Control group = 8 (17%)

Retrospective cohort study

IV iron group = 10 (11.2%)

Oral iron group = 16 (18%)

P = 0.289

Number of pre-operative transfusions received for 1:2 propensity matched IV iron group (N = 89) and oral iron group (N = 178), n (%)

IV iron group = 10 (11.2%)

Oral iron group = 30 (16.9%)

P = 0.303

Number of intra-operative transfusions received for 1:1 propensity matched IV iron group (N = 89) and oral iron group (N = 89), n (%)

IV iron group = 18 (20.2%)

Oral iron group = 33 (37.1%)

P = 0.02

Number of intra-operative transfusions received for 1:2 propensity matched IV iron group (N = 89) and oral iron group (N = 178), n (%)

IV iron group = 18 (20.2%)

Oral iron group = 72 (40.4%)

P = 0.002

Number of post-operative transfusions received for 1:1 propensity matched IV iron group (N = 89) and oral iron group (N = 89),n (%)

IV iron group = 20 (22.5%)

Oral iron group = 15 (16.9%)

P = 0.451

Number of post-operative transfusions received for 1:2 propensity matched IV iron group (N = 89) and oral iron group (N = 178), n (%)

IV iron group = 20 (22.5%)

Oral iron group = 28 (15.7%)

P = 0.237

Number of transfusions received over entire peri-operative period for 1:1 propensity matched IV iron group (N = 89) and oral iron group (N = 89), n (%)

IV iron group = 37 (41.6%)

Oral iron group = 34 (38.2%)

P = 0.759

Number of transfusions received over entire peri-operative period for 1:2 propensity matched IV iron group (N = 89) and oral iron group (N = 178), n (%)

IV iron group = 37 (41.6%)

Oral iron group = 73 (41%)

P = 1.00

Retrospective cohort study

IV treatment responsive group = 0 (0 to 15)

IV treatment unresponsive group = 2 (0 to 13); P < 0.001 vs non-anemic group; P = 0.013 vs treatment responsive group

Untreated anemic group = 2 (0 to 16); P < 0.001 vs non-anemic group; P = 0.038 vs treatment responsive group

Non-anemic group = 0 (0 to 17)

Retrospective cohort study

IV iron 1 to 300 mg group = 2.32 (1.10 to 4.93); P = 0.0280

IV iron 301 to 600 mg group = 0.77 (0.39 to 1.50); P = 0.4422

IV iron > 600 mg group = 0.97 (0.49 to 1.95); P = 0.9401

Oral iron group = 0.84 (0.49 to 1.45); P = 0.5317

Count of red blood cell units transfused for each relevant group, count ratio^b (95% CI)

IV iron 1 to 300 mg group = 1.36 (0.91 to 2.03); P = 0.1305

IV iron 301 to 600 mg group = 0.84 (0.54 to 1.31); P = 0.4414

IV iron > 600 mg group = 0.66 (0.40 to 1.10); P = 0.1151

Oral iron group = 0.66 (0.47 to 0.94); P = 0.0196

Retrospective cohort study

Anemic and received IV iron treatment group (N = 190) = 114 (60%)

Anemic and did not receive IV iron treatment or not iron deficient group (N = 581) = 368 (63.3%); P = 0.41 vs IV iron treatment group

Not anemic group (N = 2093) = 548 (26.2%); P < 0.001 vs IV iron treatment group

Median number of red blood cell units received for each group (range)

Anemic and received IV iron treatment group (N = 190) = 1 (0 to 17)

Anemic and did not receive IV iron treatment or not iron deficient group (N = 581) = 1 (0 to 13); P = 0.29 vs IV iron treatment group

Not anemic group (N = 2093) = 0 (0 to 31); P < 0.001 vs IV iron treatment group

Prospective cohort study

Anemic, iron deficient and IV iron treatment group = 2 (0.3)

Iron deficient and IV iron treatment group = 1.4 (0.4)

Anemic and no treatment group = 2.5 (0.2)

Not anemic and no treatment group = 1 (0.1)