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While autologous blood is commonly predonated to provide replacement of blood lost in orthopaedic procedures, few studies of patients managed with total joint replacement have addressed the problem of which patients are likely to benefit from an autologous blood-donation program.A retrospective analysis of 489 consecutive patients who had had a total joint arthroplasty was performed to identify the risk factors for allogenic transfusion and to further define the indications for preoperative autologous blood donation. The operations included 247 total knee replacements (157 unilateral primary, thirty-two revision, and twenty-nine one-stage bilateral primary procedures) and 271 total hip replacements (163 primary and 108 revision procedures). Fifty-four percent (264) of the 489 patients donated a total of 527 units of blood (average, 2.0 units per patient) preoperatively.One hundred and ninety-one patients (39 percent) required a transfusion of autologous blood or allogenic blood, or both. One hundred and thirty-one patients (27 percent) received autologous blood, and eighty-two patients (17 percent) received a transfusion of allogenic blood; twenty-two patients (4 percent) received both autologous and allogenic blood. Neither form of transfusion caused serious complications. Fifty-six percent (295) of the 527 units of autologous blood were discarded.Autologous donation significantly decreased the requirements for allogenic transfusion (relative risk, 0.1; p < 0.0001). It also caused the level of hemoglobin to decrease an average of 12.2 grams per liter from the time before donation to the time before the operation (p < 0.0001). Factors that increased the risk for allogenic transfusion were a revision knee or hip procedure or a one-stage bilateral primary knee replacement (relative risk, 5.7; p < 0.0001), an initial hemoglobin level of less than 130 grams per liter (relative risk, 5.6; p < 0.0001), and an age of sixty-five years or older (relative risk, 2.8; p = 0.02). None of the sixty-seven patients who had a primary knee or hip arthroplasty and an initial hemoglobin level of 150 grams per liter or more required an allogenic transfusion. In addition, none of the sixty-three patients who had a primary arthroplasty, an initial hemoglobin level of between 130 and less than 150 grams per liter, and an age of less than sixty-five years required an allogenic transfusion. Eighty-three percent (115) of the 138 autologous units donated by the seventy patients in these two groups were discarded. These wasted units accounted for 39 percent of the 295 discarded units for the entire study sample.The efficiency of collection of autologous blood can be improved by identifying patients who have a very low risk of transfusion according to the type of arthroplasty, the initial level of hemoglobin, and age. Patients who have an initial hemoglobin level of at least 150 grams per liter or an initial hemoglobin level of between 130 and 150 grams per liter and an age of less than sixty-five years have a minimal risk of needing a transfusion during or after a primary total joint replacement. These patients should be apprised of their low risk so that they can make an informed decision regarding preoperative autologous donation.