Background The pneumonia severity index (PSI) scoring system is one of the tools used to evaluate and predict the prognosis of patients with community-acquired pneumonia (CAP). Although PSI has been widely used in clinical studies of pneumonia, it is still rare to combine it with blood indexes to predict the prognosis of pneumonia. Neutrophil-to-lymphocyte ratio (NLR) is a promising candidate predictor of mortality in CAP patients. The aim of this study was to investigate the efficacy of pneumonia severity index combined with NLR in predicting 30-day mortality in CAP patients. Methods We conducted a retrospective study. We analyzed data on 400 non-immune individuals over the age of 18 in this study. All patients received blood routine measurement and PSI score calculation after admission. The primary outcome measures were mortality and survival in CAP patients. The sensitivity and specificity of PSI score, NLR, and the combination of PSI score and NLR in predicting 30-day mortality were assessed using the subject operating characteristic curve (ROC). Results Data from 400 patients were analyzed, in which the 30-day mortality was 10.5% (42/400). The AUC of NLR and PSI in predicting 30-day mortality of CAP patients were 0.81 (95% CI 0.73 - 0.89) and 0.94 (95% CI 0.90 - 0.98), respectively, with statistically significant differences (p = 0.00). The sensitivity and specificity of NLR were 0.80 and 0.7, respectively. The sensitivity and specificity of PSI were 0.78 and 0.94, respectively. The combined AUC of the two indicators for predicting death in CAP patients was 0.95 (95% CI 0.92 - 0.99), and the sensitivity and specificity were 0.85 and 0.94, respectively. Conclusions Neutrophil-to-lymphocyte ratio improves the accuracy and sensitivity of the pneumonia severity index in predicting 30-day mortality of CAP patients.
