Association Between Admission Prognostic Nutritional Index and Pulmonary Infection Status in Hospitalized Lung Cancer Patients: A Retrospective Cohort Study

Objective: To evaluate the association of the admission Prognostic Nutritional Index (PNI) with concomitant pulmonary infection and in-hospital mortality in hospitalized lung cancer patients. Methods: In this retrospective cohort study, 417 lung cancer patients admitted between December 2022 and November 2023 were categorized into those with (n=218) and without (n=199) concomitant pulmonary infection based on clinical, radiological, and microbiological evidence within 48 hours of admission. The PNI and other inflammatory indices, including the systemic immune-inflammation index (SII), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and monocyte-to-lymphocyte ratio (MLR), were calculated from admission laboratory data. Multivariable logistic regression [adjusted for age, sex, cancer stage, chronic obstructive pulmonary disease (COPD), etc.] and receiver operating characteristic (ROC) analyses were used. Results: Patients with concomitant pulmonary infection had significantly lower PNI (median: 45.03 vs. 47.25, P < 0.001) and higher SII (median: 724.00 vs. 448.00, P < 0.001) compared to those without infection. Lower PNI (aOR: 0.964, 95% CI: 0.942-0.986) and higher SII (aOR: 1.001, 95% CI: 1.000-1.001) were independently associated with concomitant infection. Among infected patients, non-survivors had significantly lower PNI (mean: 39.85 vs. 46.67, P < 0.001) and higher MLR (median: 0.50 vs. 0.32, P < 0.001) compared to survivors. Lower PNI (aOR: 0.854, 95% CI: 0.796-0.916) and higher MLR (aOR: 1.377, 95% CI: 1.026-1.849) were independently associated with in-hospital mortality. The combination of PNI and MLR achieved an AUC of 0.806 (95% CI: 0.747-0.857) for mortality discrimination. Conclusion: Admission PNI is significantly associated with concomitant pulmonary infection and independently associated with in-hospital mortality in infected lung cancer patients. Combining PNI with SII or MLR may enhance risk stratification and nutritional-immunological assessment in this vulnerable population.