Lactate to albumin ratio and 30-day mortality in ICU patients with influenza: a single-center retrospective cohort

BACKGROUND: The influenza virus exerts a substantial impact on morbidity, mortality, and overall disease burden among the population, particularly among intensive care unit (ICU) patients. Although multiple biomarkers have been studied for mortality risk stratification in this population, the prognostic relationship of the lactate-to-albumin ratio (LAR) remains incompletely defined in critically ill patients with influenza. This study aims to investigate whether baseline ICU admission LAR levels are independently associated with mortality in critically ill patients with influenza cases and assess its incremental predictive value beyond established scoring systems. METHODS: Utilizing data from the Medical Information Mart for Intensive Care IV database (MIMIC-IV, version 3.1), this retrospective cohort study enrolled adult patients diagnosed with influenza who required ICU admission. LAR was calculated based on lactate and albumin levels measured within 24 h of ICU admission. The primary outcome was 30-day mortality, with secondary outcomes including in-hospital, 60-day, 90-day, and 1-year mortality. The association between LAR and mortality risk was assessed using univariate and multivariate Cox proportional hazards regression models, with robustness evaluated through subgroup analyses and sensitivity analyses. Survival differences across LAR levels were compared via Kaplan-Meier curves and log-rank tests. Discriminative performance was assessed using receiver operating characteristic (ROC) curves and the C-index. RESULTS: A total of 142 critically ill patients with influenza were included, with an overall 30-day mortality of 22.53%. Univariate Cox regression analysis demonstrated that a higher LAR was associated with an increased risk of 30-day mortality in ICU patients with influenza (HR 2.43, 95% CI 1.80-3.29; P < 0.001). After adjusting for confounding factors, multivariable Cox proportional hazards analysis confirmed this association, showing a similarly elevated risk (HR 2.93, 95% CI 1.95-4.39; P < 0.001). Kaplan-Meier analysis indicated a substantially lower 30-day survival for the high-LAR group (Log-rank P < 0.0001). The AUC of LAR for predicting mortality was 0.783, comparable to APS III (AUC 0.785, 95% CI 0.696-0.874; P = 0.140), SAPS II (AUC 0.717, 95% CI 0.617-0.817; P = 0.157), OASIS (AUC 0.643, 95% CI 0.531-0.756; P = 0.168), and SOFA (AUC 0.687, 95% CI 0.580-0.794; P = 0.160). Notably, the AUC for albumin alone was 0.791, compared with 0.783 for LAR. CONCLUSION: This study found that early LAR upon ICU admission is independently associated with the 30-day mortality rate in critically ill patients with influenza. Its predictive ability seems to be comparable to established clinical scoring systems. However, LAR did not outperform albumin alone, and its added prognostic value beyond albumin remains uncertain, and further validation in prospective studies is still needed.