Boshkov 2006.

Methods	Design: Parallel group RCT Country: USA Multicentre study: Yes (three centre trial) Setting: Hospital Follow‐up: 2 to 12 months Unit of allocation: Patients Unit of analysis: Patients
Participants	Inclusion criteria: Undergoing coronary artery bypass grafting, cardiac valve replacement or a combination of the two. Exclusion criteria: Not reported in the abstract Patients enrolled: Not clearly reported in the abstract. Patients randomised: 1226. Prestorage leukoreduced RBC (LR‐RBCs): The number of patients is not clearly reported in the abstract. Standard RBCs (S‐RBCs): The number of patients is not clearly reported in the abstract. Patients transfused: 562. Patients considered for the analysis: Not clearly reported in the abstract. Main characteristics of patients: "Groups were statistically equivalent demographically and by all Society of Thoracic Surgery risk criteria".
Interventions	Experimental: LR‐RBCs (pre‐storage leukoreduction). Control: S‐RBCs. Co‐intervention: not reported in the abstract
Outcomes	Primary: Operative and postoperative mortality at 60 days after surgery. Secondary: Not reported in the abstract.
Notes	Trial registration: Not reported in the abstract Funding: Not reported in the abstract Role of sponsor: Not reported in the abstract A priori sample size estimation: Not reported in the abstract Conducted: Not reported in the abstract Declared conflicts of interest: "No relevant conflicts of interest to declare" (reported in the abstract) Other relevant information: All study characteristics were obtained from the abstract. We tried to contact two trial authors by email, but no response has not yet been obtained
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "patients (undergoing coronary artery bypass grafting, cardiac valve replacement, or a combination of the two) were pre‐operatively randomised to receive either LR‐ or S‐RBCs (Abstract). Insufficient information to permit judgement of ‘low risk’ or ‘high risk’.
Allocation concealment (selection bias)	Unclear risk	Comment: Insufficient information to permit judgement of ‘low risk’ or ‘high risk’.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "Patients and clinicians were blinded as to product type" (Abstract). The blinding methods are not clearly reported.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "Patients and clinicians were blinded as to product type" (Abstract). Comments: No blinding or incomplete blinding, but the review authors judge that the outcome is not likely to be influenced by lack of blinding.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	"562 patients (45.8%) were transfused: 304 received LR‐RBCs and 258 S‐RBCs" (Abstract) Loss after transfusion: Not reported in the abstract Loss after transfusion LR group: Not reported in the abstract Loss after transfusion Control group: Not reported in the abstract Loss after transfusion. Imbalance between comparison groups: Not reported in the abstract. Comment: Insufficient reporting of attrition/exclusions to permit judgement of ‘low risk’ or ‘high risk’ (e.g. number randomised not stated, no reasons for missing data provided).
Selective reporting (reporting bias)	Unclear risk	Comment: Insufficient information to permit judgement of ‘low risk’ or ‘high risk’ (Abstract data).
Other bias	High risk	Design bias: 1226 patients randomised; only 562 (45.8) were transfused.