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In patients undergoing total knee replacement (TKR), most of the measured blood loss occurs during the postoperative period, and 30-50% of these patients receive allogeneic blood transfusion (ABT). For this reason, the salvage and return of unwashed filtered shed blood (USB) from postoperative drainage may represent an alternative to ABT in these patients. We have, therefore, evaluated the clinical utility of USB return in TKR patients, with a special focus on patients with mild anaemia.Data from 200 TKR patients (group 2) receiving USB within the first 6 postoperative hours (ConstaVac CBC II, Sryker) were prospectively collected. A retrospective series of 100 TRK patients served as the control group (group 1).USB return was possible in 162 patients who received a mean of 0.98+/-0.4 U/pte, without any clinically relevant incident. Return of USB decreased both the percentage of patients with ABT (48% vs 11%, for groups 1 and 2, respectively; p0.01) and the ABT units/patient index (1.31+/-1.27 vs 0.29+/-0.87 units/patient, respectively; p0.01). A transfusion protocol was not established, but there was no difference between groups with respect to either perioperative Hb levels or overall transfusion index, indicating that the transfusion criteria were uniform. However, for the subgroups of patients who needed ABT, the preoperative Hb level was 1 g/dL lower in those receiving USB (13.4+/-1.4 vs 12.4+/-1.2 g/dL; p0.05). There was no difference in the postoperative complication rate, and patients in group 2 recovered the ability to walk 1 day earlier, and their hospital stay was 3 days shorter than in group 1 (p0.01).Return of USB after TKR seems to shorten the hospital stay and effectively reduce postoperative requirements for ABT, especially in patients with preoperative Hbor = 13 g/dL. For patients with preoperative Hb13 g/dL, although the return of USB also decreased the requirements for ABT, a further reduction will probably be obtained with the addition of another blood-saving method.