Nathens 2006.

Methods	Design: Parallel group RCT Country: USA Multicentre study: No Setting: Hospital Follow‐up: 28 days after randomisation Unit of allocation: Patients Unit of analysis: Patients
Participants	Inclusion criteria: Age of above 17 years and red cell transfusion within 24 hours of injury Exclusion criteria: Those with an anticipated survival of less than 48 hours, active infection at presentation, receipt of blood products for the current injury before randomisation, individuals with blood group AB Rh negative or B Rh negative, patients with clinically significant red cell alloantibodies requiring an antiglobulin crossmatch, recipients with prior requirements for irradiation, leukoreduction, od CMV protection, subjects enrolled in a concurrent study of pre‐hospital hypertonic saline resuscitation or incarcerated subjects. Patients enrolled: 1864 Patients randomised: 1864 Standard transfusion: 935 Leukoreduced transfusion: 929 Patients transfused: 515 Patients considered for the analysis: 324 Main characteristics of patients included in full analysis. Age: Standard group = 42.1 ± 18 years; Leukoreduced group = 42.3 ± 19 years Percentage of men: Standard group = 69%; Leukoreduced group = 66% Percentage of penetrating injury mechanism: Standard group = 18%; Leukoreduced group = 19% Injury Severity Score: Standard group = 25.5 ± 11; Leukoreduced group = 23.9 ± 11
Interventions	Leukoreduced transfusion: Prestorage‐Leucoreduced RBC (pre‐storage leukoreduction). Standard transfusion: Non Prestorage‐Leucoreduced RBC (standard units). Cointerventions: "All patients received apheresis platelets when platelets were required" (Page 343).
Outcomes	Primary: Infection within 28 days of randomisation. Secondary: Resource use: ventilator days, lengths of hospital stay and length of ICU. Degree of multiple organ dysfunction. Mortality. Note: TRALI was assessed by Watkins 2008 as a secondary analysis.
Notes	Trial registration: www.clinicaltrials.gov, August 23, 2005. Registration No.: NCT00135291 Funding: National Institutes of Health (NIH) Role of sponsor: The sponsor had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review or approval of the manuscript. A priori sample size estimation: Yes Conducted: Between 3 February 2003 and 30 August 2004. Declared conflicts of interest: Not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The hospital‐based transfusion support service performed the randomization in a 1:1 ratio, using a permuted block scheme (block size of six)" (Page 344).
Allocation concealment (selection bias)	Low risk	Quote: "Using preprinted sealed opaque envelopes containing the study identification number and randomization arm (listed as arm 1 or arm 2) to conceal allocation" (Page 344).
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "Before unit issue, the transfusion service added a Food and Drug Admnistration approved study label to blind the leukoreduction process; the transfusion report accompanying the red cell unit was also blinded" (Page 343).
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "Before unit issue, the transfusion service added a Food and Drug Admnistration approved study label to blind the leukoreduction process; the transfusion report accompanying the red cell unit was also blinded" (Page 343).
Incomplete outcome data (attrition bias) All outcomes	Low risk	Loss after transfusion: 5% (16/324). Loss after transfusion LR group: 7% (11/156). Loss after transfusion Control group: 3% (5/168). Imbalance between comparison groups: 4%.
Selective reporting (reporting bias)	Low risk	Comments: The study protocol is available and all of the study's pre‐specified (primary and secondary) outcomes that are of interest in the review have been reported in the pre‐specified way.
Other bias	Low risk	Comment: The study appears to be free of other sources of bias.