Peak Lactate During the First Postoperative Day Predicts 90-Day Graft Loss After Liver Transplantation

Background: Early identification of liver transplant (LT) recipients at risk of graft failure is crucial to allow timely retransplantation. Lactate levels have been proposed as markers of graft dysfunction, although their optimal timing and predictive value remain uncertain. This study aimed to investigate the prognostic role of early postoperative lactate measurements for predicting 90-day graft loss after LT and compare their performance with established early allograft dysfunction scores. Methods: This retrospective observational study included adult patients undergoing their first LT at the Sapienza University of Rome (Italy) between 2013 and 2021, with external validation in an independent cohort from Zagreb University (Croatia) between 2022 and 2025. Lactate levels were evaluated at declamping, at the end of transplantation, and as the peak value within the first postoperative day. Their predictive ability for 90-day graft loss was compared with Early Allograft Dysfunction (EAD) and the Model for Early Allograft Function (MEAF) score using receiver operating characteristic (ROC) analysis. Results: A total of 268 LT recipients were analyzed (178 Sapienza and 90 Zagreb). Ninety-day graft loss occurred in 25 (14.0%) patients in Sapienza and 10 patients (11.1%) in Zagreb. A lactate peak within the first postoperative day showed the highest discriminative ability for predicting graft loss in both cohorts (Sapienza: AUC 0.87, 95%CI 0.77-0.98, p < 0.001; Zagreb: AUC 0.79, 95%CI 0.62-0.97, p = 0.003). This outperformed EAD and MEAF. A lactate peak cutoff of 5.0 mmol/L (75th percentile) resulted in 80.0% sensitivity and 86.3% specificity in Sapienza and 80.0% sensitivity and 68.7% specificity in Zagreb. Higher thresholds increased specificity, reaching 98.7% and 95.0% at 8.4 mmol/L in the Sapienza and Zagreb cohorts, respectively. Patients with a lactate peak ≥ 5.0 mmol/L showed significantly higher 90-day graft loss compared with those below the threshold in both cohorts (Sapienza: 47.6% vs. 4.7%, p < 0.001; Zagreb: 25.0% vs. 5.0%, p = 0.004). Conclusions: The peak lactate value during the first postoperative day represents a simple and accurate biomarker for predicting early graft loss after LT. Its superior predictive performance compared with commonly used EAD-related scores suggests that the lactate peak may represent a valuable tool for early postoperative risk stratification.