<p>Variables with missing values exceeding 20%.</p>

Background This study aimed to explore the nonlinear positive correlation between the glucose-to-lymphocyte ratio (GLR) and increased risk of in-hospital mortality and ICU mortality in critically ill patients with pneumonia. Methods This was a retrospective observational cohort study and data were obtained from the Medical Information Mart for Intensive Care-IV (MIMIC IV) database and eICU-Collaborative Research Database (eICU-CRD) database. The primary outcome was in-hospital mortality and ICU mortality.According to the GLR, the participants were divided into quartiles (Q1–Q4).Kaplan–Meier analysis was used to compare the mortality of the above four groups.Multivariate Cox regression analysis and restricted cubic spline regression was used to evaluate the association between GLR and in-hospital mortality and ICU mortality in patients with pneumonia. In addition, the data of patients with bacterial pneumonia were extracted using MIMIC-IV database, and Kaplan-Meier analysis and Cox regression analysis were also used. Results 1,961 patients from the MIMIC-IV cohort were included. Logistics regression analysis showed that an elevated GLR was significantly associated with all-cause mortality. After adjusting for confounding factors, patients with an elevated GLR showed a significant correlation with in-hospital mortality [HR (95% CI): 1.84 (1.36–2.51), p < 0.001] and ICU mortality [HR (95% CI): 1.47 (1.04–2.17), p = 0.049]. Kaplan-Meier survival analysis curves indicated that patients with higher GLR levels had significantly lower survival probabilities. The restricted cubic spline regression model revealed that a nonlinear positive correlation between GLR levels and increased risk of death among patients with pneumonia.6,405 patients from the eICU-CRD cohort were included. Logistics regression analysis showed that, after adjusting for confounding factors, patients with an elevated GLR had a significant association with in-hospital mortality [HR (95% CI): 1.18 (1.00–1.38), p = 0.047]. The Kaplan-Meier survival analysis curves indicated that patients with higher GLR levels had significantly lower survival probabilities. The restricted cubic spline regression model revealed that a nonlinear positive correlation between GLR levels and increased risk of death among patients with pneumonia.Furthermore, data extracted from the MIMIC-IV cohort demonstrated that the predictive performance of GLR for all-cause mortality remained robust among patients with bacterial pneumonia. Conclusions GLR is significantly associated with increased all-cause mortality in patients with pneumonia. This finding suggests that GLR may help identify people with pneumonia at high risk of mortality.