ObjectivesWe aimed to rapidly predict the prognosis of patients who present to the emergency department (ED) with acute gastrointestinal bleeding (AGIB) using point-of-care (POC) lactate testing. MethodsThis single-center retrospective observational study included 327 patients (survival group, 287; non-survival group, 40) who presented to the ED with AGIB between March 2021 and February 2022. We compared POC-measured lactate levels with laboratory-measured lactate levels using Pearson's correlation. Multivariate logistic regression analysis was used to identify early predictors of in-hospital mortality and correlated clinical outcomes. Receiver operating characteristic (ROC) curves were used to determine the optimal cutoff for POC-measured lactate levels for predicting in-hospital mortality, and the ROC curves for POC-measured lactate levels and AIMS65 scores were compared using the DeLong test. ResultsPOC-measured lactate levels strongly correlated with laboratory-measured lactate levels (R2 = 0.82). Patients in the non-survival group had higher POC-measured lactate levels than did those in the survival group (2.6 mmol/L vs. 1.4 mmol/L, p < 0.001). POC-measured lactate level, age, systolic blood pressure, heart rate, and malignancy were identified as early predictors of in-hospital mortality (adjusted odds ratio [aOR] for POC-measured lactate levels: 1.15; 95 % confidence interval [CI] 1.02–1.30). The optimal POC-measured lactate level cutoff was 3.2 mmol/L. Areas under the ROC curves for POC-measured lactate level and the AIMS65 score were 0.70 and 0.73, respectively, showing statistical compatibility. Higher POC-measured lactate levels correlated with ICU admission, blood transfusion, and mechanical ventilation (aOR: 1.16, 95 % CI 1.05–1.27; 1.16, 1.04–1.30; and 1.31, 1.13–1.53, respectively]. Further, the hyperlactatemia subgroup (POC-measured lactate level ≥3.2 mmol/L) exhibited a lower survival probability in the Kaplan–Meier survival analysis (p < 0.01). ConclusionsOur study shows that rapidly obtainable POC-measured lactate levels are valuable for predicting critical outcomes in AGIB patients and should be considered an early prognostic indicator for in-hospital mortality in the ED.