Comparison of VTE prophylaxis agents on hemoglobin levels after total knee arthroplasty: a hospital information system-based observational study

BACKGROUND: While venous thromboembolism (VTE) prophylaxis is crucial following major orthopaedic surgeries including total knee arthroplasty (TKA), the impact of different prophylactic agents on postoperative hemoglobin (Hb) levels remains inadequately studied. The aim of this study was to compare the effects of aspirin, rivaroxaban, and low-molecular-weight heparin (LMWH) on early postoperative Hb changes following TKA. METHODS: In this single-center retrospective cohort study, 655 primary TKAs were finally included using data from the hospital information system. Patients received either aspirin, rivaroxaban, or LMWH for VTE prophylaxis. The primary outcome was the magnitude of Hb reduction, calculated as the difference between the Hb level on the first postoperative day and the minimum postoperative Hb level before discharge. The secondary outcome was the trajectory of postoperative Hb changes within the first week. RESULTS: Postoperative Hb levels clearly declined within the first week, with a mean of 13.9 g/L (SD, 8.5) from postoperative day 1 in the entire cohort. In the fully adjusted linear regression model, both rivaroxaban (β = 1.5, [95%CI, 0.0 to 3.0]) and low-molecular-weight heparin (LMWH) (β = 3.3, [95%CI, 1.5 to 5.2]) were associated with a greater reduction in Hb compared to aspirin. Regarding the trajectory of postoperative Hb changes, the generalized additive mixed model revealed no statistically significant difference between rivaroxaban and aspirin (β = -0.2, [95%CI, -0.6 to 0.2]). LMWH was associated with a greater daily reduction in Hb levels relative to aspirin, averaging 0.8 g/L per day (β = -0.8, [95%CI, -1.3 to -0.3]). Despite these observed differences, the effect sizes were small, suggesting a lack of clinical significance. CONCLUSIONS: Hemoglobin levels declined significantly following TKA within the first week after surgery. However, no clinically meaningful distinction is discernible between the three most frequently used pharmacological agents, aspirin, rivaroxaban and LMWH. LEVEL OF EVIDENCE: III, A retrospective cohort study.