Lactate-to-Albumin Ratio Predicts Mortality in Patients with Sepsis-Associated ARDS: A Dual-Cohort Retrospective Study

Background: Sepsis-associated acute respiratory distress syndrome (ARDS) is a common and highly fatal complication in the intensive care unit. The lactate-to-albumin ratio (LAR), a composite biomarker that integrates information on tissue perfusion, oxidative stress, and inflammatory status, has been demonstrated to correlate with prognosis in various critical illnesses. However, its prognostic value in the specific population of patients with sepsis-associated ARDS has not yet been systematically validated in large-scale cohorts. Method: This study was a retrospective cohort analysis based on 5,240 patients from the MIMIC-IV database (primary cohort) and 396 patients hospitalized at the Affiliated Hospital of Guangdong Medical University (validation cohort). All patients were stratified into four groups (Q1–Q4) according to the quartiles of their first LAR value measured within 24 hours of admission. A multivariable Cox proportional hazards regression model was used to evaluate the association between LAR and 28-day all-cause mortality. Restricted cubic spline (RCS) analysis, Kaplan–Meier survival curves, and subgroup analyses were further employed to validate its independent predictive value and robustness. Result: In the multivariable-adjusted models, elevated LAR was independently associated with an increased risk of 28-day mortality (primary cohort: HR = 1.09, 95% CI 1.05–1.13, P < 0.001; validation cohort: HR = 2.87, 95% CI 1.21–6.82, P = 0.017). Restricted cubic spline analysis suggested a nonlinear positive association between LAR and mortality, and Kaplan–Meier curves demonstrated a significant decrease in survival with increasing LAR quartiles (log-rank P < 0.001). Subgroup analysis indicated that the predictive value of LAR was generally consistent across patients with different clinical characteristics. Conclusion: In patients with sepsis-associated ARDS, an elevated LAR early after admission is an independent risk factor for 28-day all-cause mortality. As an easily accessible composite index, LAR may integrate dual pathophysiological information reflecting both hypoxic stress and systemic inflammation/catabolic state. This facilitates early identification of high-risk patients and underscores its potential clinical utility as a prognostic biomarker.