van Hilten 2004.

Methods	Design: Parallel group RCT Country: The Netherlands Multicentre: Yes, 19 hospitals (3 university, 10 clinical, 6 general) Setting: Hospital Follow‐up: 15 months Unit of allocation: Patients Unit of analysis: Patients
Participants	Inclusion criteria: Patients with ruptured aortic aneurysm elective non‐ruptured AA surgery or gastrointestinal oncology) Exclusion criteria: Those aged under 18 years, had received transfusions in the three month before the date of randomisation, or had a previous adverse reaction to blood transfusions or had a specific indications for filtered products. Patients enrolled: 1200 Patients randomised: 1200 Non‐filtered products: 605 Filtered products: 595 Patients transfused: 494 Patients considered for the analysis: 1051 Main characteristics of patients allocated to groups (transfused+non‐transfused): Age: Non‐filtered group = 67 ± 11 years; Filtered group = 66 ± 11.5 years Percentage of men: Non‐filtered group = 69%; Filtered group = 68% Percentage of patients transfused: Non‐filtered group = 53%; Filtered group = 51% Duration of surgery: Non‐filtered group = 210 min; Filtered group = 205 min
Interventions	Experimental group: Filtered RBC transfusions (pre‐storage leukoreduction). Control group: Non‐filtered RBC transfusions. (buffy coat removed and were plasma reduced).
Outcomes	Primary: Mortality and duration of stay in intensive care. Secondary: Multi‐organ failure. Infections. Length of hospital stay.
Notes	Trial registration: www.clinicaltrials.gov, 23 August 2005. Registration No.: NCT00135291 Funding: Health insurance Board, the Netherlands, The National Sanquin Bllod banks. Role of sponsor: Not reported A priori sample size estimation: Yes Conducted: Since June 2000 until December 2001 Declared conflicts of interest: Yes Note: 22 patients because of administrative and logistic errors. The intake of patients in the study had to be stopped at the end of 2001 because of the implementation of universal leucocyte depletion of RBCs in The Netherlands. This measure was taken by the Dutch Ministry of Health in an effort to reduce the risk of possible transmission of variant Creutzfeldt‐Jacob disease in non‐filtered transfusions.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "randomisation was performed either by telephone (central registration of randomisation) or by opening numbered and sealed envelopes at the hospital blood transfusion services. The transfusion service ensured that the released RBCs appeared identical" (Page 2).
Allocation concealment (selection bias)	Low risk	Quote: "randomisation was performed either by telephone (central registration of randomisation) or by opening numbered and sealed envelopes at the hospital blood transfusion services. The transfusion service ensured that the released RBCs appeared identical" (Page 2).
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "Neither the identity of the patient nor the randomisation group was stored in the main database. The actual randomisation was provided to the statistician only at the final analysis. (Page 2).
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Quote: "During the study, protocol violations were reported monthly to the national trial office. Patients who received products in violation of randomisation remained in the assigned arm for intention to treat analysis." (Page 2).
Incomplete outcome data (attrition bias) All outcomes	High risk	Loss after transfusion: 9.35% (51/545). Loss after transfusion filtered RBC transfusions: 11% (30/267). Loss after transfusion non‐filtered RBC transfusions: 7.5% (21/278). Imbalance between comparison groups: 3.5%. Comment: Missing outcome data are balanced in numbers across study groups. However, reasons for missing outcome data are likely to be related to true outcome (Protocol violations).
Selective reporting (reporting bias)	Low risk	The study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre‐specified.
Other bias	High risk	Design bias.