Johnson 1992.

Study characteristics
Methods	Design: RCT, parallel 2‐arm, single‐centre trial   Setting: university teaching hospital, Boston (USA) Recruitment: not specified Maximum follow‐up: in‐hospital stay
Participants	39 autologous blood donors undergoing elective myocardial revascularisation were randomised to 1 of 2 groups: Liberal group: n = 18; M/F = 16/2; mean (SD) age = 60.5 (6.9) years Restrictive group: n = 20; M = 20; mean (SD) age = 58.2 (7.5) years
Interventions	Liberal group: received blood to achieve Hct value of 32% Restrictive (conservative) group: received blood to achieve Hct value of < 25%
Outcomes	Cardiac events, complications, postoperative blood loss, blood use (total units), allogeneic blood use (units), autologous blood use (units), all product blood use (units), number of participants receiving transfusions, mean cardiac index, mean systemic resistance, exercise capacity, Hct levels, length of ICU stay, length of hospital stay 5 days after surgery, all participants were asked to complete an exercise treadmill test. A second test was performed the following day
Notes	Funding not stated Trial registration: none ascertainable Trial funding: none specified for the trial, but 1 investigator was supported in part by Transfusion Medicine Academic Award K07HL02033 from the National Institutes of Health (Johnson 1992 p 307) COI statement by investigators: none appears in the publication
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	"All patients giving informed consent were randomized (with the aid of a table of random numbers and an odd‐even [conservative strategy‐liberal strategy] designation) to one of two postoperative transfusion strategies" (Johnson 1992 p 308)
Allocation concealment (selection bias)	Unclear risk	It is unclear if assignment was concealed before randomisation
Blinding of participants and personnel (performance bias) Objective outcomes	Low risk	Blinding of personnel for this intervention is not feasible, but in our view, for objective outcomes such as mortality (the primary outcome used within this review), we graded risk of bias as 'low' Surgeons and anaesthesiologists were said to be blinded to the group of randomisation until the participant reached the ICU
Blinding of outcome assessment (detection bias) Objective measures	Low risk	Blinding of mortality (the primary outcome used within this review) is not relevant, and we graded risk of bias as 'low'
Blinding of outcome assessment (detection bias) Subjective measures	High risk	No data from subjective outcomes (e.g. function). Exercise tolerance was assessed and reported, and risk of bias is considered unclear without more information on the assessors
Incomplete outcome data (attrition bias) All outcomes	Low risk	"Data were complete for 38/39 participants (18/18 in the liberal group; 20/21 in the restrictive group)"
Selective reporting (reporting bias)	Unclear risk	No reporting bias was apparent, but in the absence of prospective registration or a trial protocol, assessment must remain 'unclear'
Other bias	Low risk	No other biases were apparent