Methods	A prospective, randomised study was conducted to analyse differences in post-operative haemoglobin levels and allogeneic blood requirements in patients undergoing primary total hip replacement (THR). Between December 2003 and December 2005, consecutive patients undergoing elective primary THR for arthritis at Weston General Hospital were enrolled. The patients were block randomised (computer-generated) to one of two groups from sealed envelopes opened by a nurse after reduction of the prosthesis
Participants	190 patients undergoing elective primary total hip replacement were randomised to one of two groups: Group 1 (Autotransfusion group): n=76; M//F=36//40; mean (range) age = 73.5 (52-87) years Group 2 (Control group): n=82; M//F=40//42; mean (range) age = 75.5 (46-91) years NB: From the 190 patients who agreed to participate, 158 sets of complete data were obtained. There were 22 incomplete haemoglobin (Hb) values and 10 patients did not fulfil the inclusion criteria
Interventions	Group 1: Autotransfusion group had wound drainage processed by the ABTrans autologous re-transfusion system. The autologous closed circuit system included two drains and a 125 micron filter through which the blood passes through before entering the 1200ml reservoir. Autologous re-transfusion was given at 4 hourly intervals from opening of the drain or when 400mls had collected in the reservoir. The maximum time between collection and completion of each transfusion was six hours. The system was used for 24 hours or up to a total of 1600mls. Group 2: Control group received two standard Medinorm vacuum drains. The Medinorm vacuum drains were removed 48 hours after surgery.
Outcomes	Outcomes reported: number of patients transfused allogeneic blood, amount of allogeneic blood transfused, volume of blood re-transfused from the cell saver, hospital length of stay, adverse events
Notes	Transfusion threshold: the individual orthopaedic team decided whether to give allogeneic blood transfusion. Local practice was to give two units if the post-operative Hb was less than 8.0g/dL or if patients were symptomatic with Hb in the range of 8.0g/dL to 10.0g/dL
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Method used to generate allocation sequences was adequate.
Allocation concealment (selection bias)	High risk	Method used to conceal treatment allocation was inadequate.
Blinding (performance bias and detection bias) All outcomes	High risk