Postoperative Hemoglobin Thresholds Versus Estimated Blood Loss as Determinants of Blood Transfusion in Total Knee Replacement

Blood transfusion after total knee replacement (TKR) presents significant clinical and resource implications. While estimated blood loss (EBL) and estimated blood volume (EBV) have historically guided transfusion decisions, emerging trends emphasize postoperative hemoglobin (Hb) thresholds and clinical triggers. This study combines a retrospective cohort analysis with a systematic review to appraise current transfusion practices in TKR. We conducted a systematic literature search (2020–2025) in PubMed, EMBASE, and Cochrane for studies reporting transfusion triggers, thresholds, blood management strategies, and outcomes in TKR. Concurrently, we analyzed 103 TKR patients (June 2023–June 2025), evaluating perioperative Hb, EBL using Gross’ formula, EBV using Nadler’s formula, alongside clinical triggers for transfusion. Statistical analysis included Mann–Whitney U test, receiver operating characteristic (ROC) curves, and logistic regression. Among 12 eligible studies (combined N ≈ 15,000 TKR patients), mean transfusion rates ranged from 5% to 25%, depending on the use of tranexamic acid and restrictive Hb thresholds (typically 7–9 g/dL). Most institutions prioritized Hb level over EBL as a transfusion trigger, with growing incorporation of hemodynamic and symptomatic criteria. Of 103 patients, 14 (13.6%) required transfusion. Postoperative Hb near 8 g/dL (8.1 ± 0.4) was significantly associated with transfusion ( P < 0.001); EBL and EBV were not independent predictors. ROC analysis favored Hb (AUC = 0.87) over EBL (AUC = 0.62). Patient-reported outcomes were favorable, with no major morbidity. Both the literature and our cohort support postoperative Hb thresholds (≈8 g/dL), supplemented by clinical triggers, as the most reliable guidance for transfusion in TKR. Hb-guided, symptom-informed protocols align with patient safety and modern blood conservation principles.