Methods	A prospective randomised study was undertaken to quantify the effect of reinfusion of post-operative shed blood drainage on the haemoglobin levels in patients undergoing elective primary total hip arthroplasty (THA) and total knee arthroplasty (TKA). Patients were enrolled between December 1990 and August 1991. Randomisation was performed using a random number table. Allocation concealment was not described
Participants	111 patients undergoing elective primary total hip arthroplasty and total knee arthroplasty were randomly assigned to one of two groups: Group 1 (Autotransfusion system): n=57 Group 2 (Control group): n=54 NB: Mean age of TKA patients was 68 years (range 39-88 years). Mean age of THA patients was 62 years (range 27-85 years)
Interventions	Group 1: Autotransfusion group (CBC ConstaVac) had their post-operative drainage collected and filtered. The unwashed red blood cells were reinfused within a 6-hour period. The blood was reinfused through a 20um macroaggregate filter. The CBC ConstaVac system has an umbrella valve that ensures that the top 100mls of fluid containing serum fat, and bone debris does not leave the reservoir. Group 2: Control group were treated with a standard post-operative collection system. NB: All patients were encouraged to donate two units of autologous blood prior to both THA and TKA procedures
Outcomes	Outcomes reported: number of patients transfused allogeneic or autologous blood, postoperative drainage, Hb levels
Notes	Transfusion threshold: intra-operative blood transfusion was left to the discretion of the operating surgeon. No transfusion threshold or trigger was reported
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation was performed using a random number table.
Allocation concealment (selection bias)	Unclear risk	Method used to conceal treatment allocation was unclear.
Blinding (performance bias and detection bias) All outcomes	High risk