Defining Preoperative Anemia Thresholds for Revision Total Knee Arthroplasty

In an era of value-based medical management, anemia optimization before revision total knee arthroplasty (TKA) could improve outcomes. Using a simulation model, we evaluated whether outcomes would improve for revision TKA if patients were either approved/denied surgery based on incremental preoperative anemia thresholds.

We retrospectively reviewed consecutive revision TKA patients from 2019 to 2024. Exclusion criteria were primary TKA, no preoperative hematocrit, and incomplete 1-year follow-up. Simulated preoperative hematocrit cutoff values of 39 to 33% were used in a sequential manner. Preoperative hematocrit values above each threshold "met the threshold" for surgery, while hematocrit values below each threshold "did not meet the threshold" for surgery. Intraoperative transfusion, postoperative transfusion, discharge disposition, 90-day readmission, and complications were evaluated. Area under the curve (AUC) determined anemia thresholds needed for an event not to occur.

If the strictest 39% hematocrit threshold was used, 669 of 1,322 (50.6%) patients would not meet the threshold for surgery, with these patients having higher readmissions (18.2 versus 8.4%), intraoperative transfusions (13 versus 0.5%), postoperative transfusions (26.3 versus 4.1%), nonhome discharge (53.8 versus 23.7%), and postoperative complications (26.8 versus 10.6%) compared to counterparts meeting the threshold. If the most lenient 33% hematocrit threshold was used, 243 of 1,322 (18.4%) patients would not meet the threshold for surgery, with higher readmissions (23.9 versus 11%), intraoperative transfusions (31.7 versus 1.2%), postoperative transfusions (50.2 versus 7.5%), nonhome discharge (74.5 versus 31%), and postoperative complications (38.7 versus 14.3%) compared to counterparts meeting the threshold. Based on area under the curve testing, the most sensitive and specific hematocrit threshold was 33.3% for intraoperative transfusion (sensitivity 86.1%, specificity 87.8%). Similar trends were found across hemoglobin thresholds.

Setting preoperative anemia thresholds for revision TKA eligibility may have a role in reducing the likelihood of readmission, transfusion, complications, and nonhome discharge. Preoperative hematocrit thresholds consistently demonstrated high sensitivity and positive predictive value pertaining to intra- and postoperative transfusion rates. Optimization of these thresholds, when possible, may improve the likelihood of a successful outcome and maximize value-based care.