Wallis 2002.

Methods	Design: Parallel group RCT Country: UK Multicentre study: No Setting: Hospital Follow‐up: 3 months after discharge Unit of allocation: Patients Unit of analysis: Patients
Participants	Inclusion criteria: Patients admitted for elective coronary artery bypass grafting or aortic or mitral valve replacement, either singly or in combination Exclusion criteria: Those with a history of recurrent infections, had a current blood disorder, were taking steroid or other immunosuppressive drugs or received transfusions within the past 12 months Patients enrolled: 597 Patients randomised: 597 Plasma reduced group: 198 patients Buffy coat‐depleted group: 204 patients WBC filtered group: 195 patients Patients transfused: 509 Patients considered for the analysis: 597 Main characteristics of patients (included non‐transfused): Age: Plasma reduced group = 62.2 ± 9.1 years; Buffy coat‐depleted group = 62.4 ± 8.1 years. WBC filtered group = 61.7 ± 8.6 years Gender ratio (men to women): Plasma reduced group = 2.9; Buffy coat‐depleted group = 2.6; WBC filtered group= 2.9 Preoperative Hb in g/dL: Plasma reduced group = 14.2 ± 1.2; Buffy coat‐depleted group = 14.1 ± 1.2. WBC filtered group = 14.2 ± 1.2 Discharge Hb in g/dL: Plasma reduced group = 11.3 ± 0.9; Buffy coat‐depleted group = 11.3 ± 1. WBC filtered group = 11.1 ± 0.9
Interventions	Plasma reduced. Buffy coat‐depleted. WBC filtered (pre‐storage leukoreduction).
Outcomes	Primary Events coded as hospital acquired infection. Secondary: Length of hospital stay. Postoperative fever. Use of antibiotics in hospital. Evidence of infection after discharge from hospital.
Notes	Trial registration: Not reported Funding: This study was supported in part by a grant from the Northern and Yorkshire R & D directorate of the National Health Service Role of sponsor: Not reported A priori sample size estimation: Yes Conducted: Not reported Declared conflicts of interest: Not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Patients were randomly assigned to receive, in the event of a transfusion, PR, BCD, or WCF blood" (Page 1128).
Allocation concealment (selection bias)	Unclear risk	Quote: "Randomization by sealed envelopes was carried out in the hospital blood transfusion department at the time of the admission clinic" (Page 1128). Use of opaque envelopes is not reported.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: "The surgical staff were not blinded as to the blood component given, but were unaware of the randomization when the first decision to transfuse was made" (Page 1128).
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: Collection and review of data to determine postoperative infections and other variables were carried out without knowledge of the randomization or type of blood given" (Page 1128).
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: All patients transfused were analysed.
Selective reporting (reporting bias)	Low risk	The study protocol is unavailable but it is clear that the published reports include all expected outcomes, including those that were pre‐specified (convincing text of this nature may be uncommon).
Other bias	Low risk	Comment: The study appears to be free of other sources of bias.