Delta hemoglobin cutoffs do not predict readmission in patients undergoing primary simultaneous bilateral total hip or knee arthroplasty: A retrospective cohort study.

Background/aims: Primary simultaneous bilateral total joint arthroplasty (simBTJA) can cause postoperative anemia. Clinicians might hesitate to discharge patients who have large changes in hemoglobin [Hgb], despite Hgb levels remaining above transfusion thresholds. This study was conducted to evaluate if delta Hgb or perioperative blood loss correspond with readmission in primary simBTJA patients not transfused perioperatively. Methods: From 2015 - 2020, a retrospective chart review of primary simultaneous bilateral total hip/knee arthroplasty cases was conducted. Preoperative and postoperative Hgb levels were obtained from our database or chart review. Exclusion criteria comprised patients who had a preoperative transfusion or transfusion postoperatively during their surgical admission, and patients not discharged home. Outcomes included whether delta Hgb or perioperative blood loss were predictive of 90-day readmission postoperatively, postoperative anemia, and transfusion during readmission. Results: The 510 individuals undergoing primary simBTJA possessed an average preoperative Hgb of 14.1 g/dL, starting blood volume of 5012 mL, postoperative Hgb of 10.0 g/dL, delta Hgb of 3.90 g/dL, and perioperative blood loss of 1403 mL. 19 patients (3.73 %) were readmitted, with none requiring transfusion. When constructing receiver operating characteristic (ROC) curves predicting readmission from delta Hgb, a threshold of 4.1 g/dL had an area under the curve (AUC) of 0.454, a sensitivity of 0.473, and a specificity of 0.56. For ROC curves predicting readmission from perioperative blood loss, a threshold of 1144 mL had an AUC of 0.453, a sensitivity of 0.842, and a specificity of 0.297. Similar AUCs, sensitivities, and specificities were obtained when adjusting ROC curves for preoperative Hgb or starting blood volume. Conclusions: Delta Hgb and perioperative blood loss do not predict 90-day readmission after primary simBTJA in patients not transfused perioperatively. Patients with a large delta Hgb but stay higher than a 7 g/dL restrictive transfusion threshold may have a strong capacity to overcome postoperative anemia.