Tartter 1998.

Methods	Design: Parallel group RCT Country: USA Multicentre study: No Setting: Hospital Follow‐up: Unclear. Quote: "Patients were followed up daily in the hospital until discharge (...) and contacted by phone following discharge to elicit possible symptoms of infection". Unit of allocation: Patients Unit of analysis: Patients
Participants	Inclusion criteria: Those scheduled for inpatient gastrointestinal surgery under general anaesthesia Exclusion criteria: Not clearly reported Patients enrolled: 224 Patients randomised: 224 Filtered group: 106 Unfiltered group: 118 Patients transfused: 59 Patients considered for the analysis: 221 Main characteristics of patients: Age (Unclear if median or mean): Filtered group = 54 years; Unfiltered group = 50 years Percentage of men: Filtered group = 49%; Unfiltered group = 50% Hematocrit (Unclear if median or mean): Filtered group = 38; Unfiltered group = 37 Percentage of hypertension: Filtered group = 14%; Unfiltered group = 10% Percentage of diagnosis of malignancy: Filtered group = 38%; Unfiltered group = 38%
Interventions	Filtered group: Leukocyte‐filtered RBCs (the timing of leukoreduction is not reported). Unfiltered group: PRBCs. Cointerventions: "Preoperative preparation included intravenous antibiotics for all patients and bowel cleansing with Golytely for patients in whom transection of the colon or rectum was anticipated" (Page 463)
Outcomes	This RCT did not specify by primary or secondary outcomes. Postoperative infectious complications: abdominal wound infections, urinary tract infections, Pneumonia, intra‐abdominal collections. Length of stay Hospital charges.
Notes	Trial Registration: Not reported. Funding: Pall Corporation, Gel Cove, NY Role of sponsor: Not stated. A priori sample size estimation: Unclear. Trial authors reported the criteria for sample size calculation, including a 60% of dropout rate ("40% of gastrointestinal surgery patients at our institution receive blood transfusions"). The software or method for sample size calculation is not reported. Using the ARCSINUS approximation, and using the same criteria reported by authors, 174 subjects are necessary in first group and 174 in the second to find as statistically significant a proportion difference, expected to be of 0.2 in group 1 and 0.05 in group 2, with an anticipated drop‐out rate of 60%. The study included 224 participants (118 and 106 patients in each group), 59 were transfused (26%) and 50 participants received allogeneic RBC transfusions. Conducted: Between 1 August 1993 and 31 January 1994 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 allocated by the study personnel in the blood bank" (Page 463). Comment: 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	Comment: Insufficient information to permit judgement of ‘low risk’ or ‘high risk’.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: Insufficient information to permit judgement of ‘low risk’ or ‘high risk’.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: all patients transfused were analysed (Page 842).
Selective reporting (reporting bias)	High risk	This RCT did not report mortality. Comment: The study report fails to include results for a key outcome that would be expected to have been reported for such a study.
Other bias	High risk	Design bias. Sample size bias. Trial authors reported the criteria for sample size calculation, including a 60% of dropout rate ("40% of gastrointestinal surgery patients at our institution receive blood transfusions"). The software or method for sample size calculation is not reported. Using the ARCSINUS approximation, and using the same criteria reported by the study authors, 174 subjects are necessary in first group and 174 in the second to find as statistically significant a proportion difference, expected to be of 0.2 in group 1 and 0.05 in group 2, with an anticipated drop‐out rate of 60%. The study included 224 participants (118 and 106 patients respectively), 59 were transfused (26%) and 50 participants received allogeneic RBC transfusions.