Prognostic Nutritional Index and 30-Day Mortality in Hospitalized Community-Acquired Pneumonia: A Retrospective Cohort Comparison with PSI and CURB-65

Background: The Prognostic Nutritional Index (PNI), derived from serum albumin and peripheral lymphocyte count, may reflect immunonutritional status in patients with community-acquired pneumonia (CAP). This study evaluated the association between admission PNI and 30-day mortality and compared its discriminatory performance with the Pneumonia Severity Index (PSI) and CURB-65. Methods: This retrospective single-center cohort included 214 adults hospitalized with CAP between January 2025 and June 2026. Demographic, clinical, and laboratory data obtained at admission were analyzed. Thirty-day all-cause mortality was the primary outcome. Receiver operating characteristic analysis and multivariable logistic regression were performed. Results: Thirty-day mortality occurred in 61 patients (28.5%). PNI was significantly lower in non-survivors than survivors (34.5 ± 5.6 vs. 39.1 ± 6.4; p < 0.001). PNI showed moderate discrimination for 30-day mortality (AUC 0.713, 95% CI 0.637–0.789), with a numerically higher AUC than PSI (0.656) and CURB-65 (0.670); however, pairwise differences were not statistically significant. A cohort-derived exploratory PNI cutoff of ≤36.6 yielded 70.5% sensitivity and 67.3% specificity. In multivariable analysis, continuous PNI remained independently associated with mortality (OR 0.869 per one-unit increase, 95% CI 0.814–0.927; p < 0.001). Adding PNI significantly improved discrimination compared with PSI alone (AUC 0.740 vs. 0.656; p = 0.034) and CURB-65 alone (AUC 0.771 vs. 0.670; p = 0.001). Conclusions: Lower admission PNI was independently associated with 30-day mortality and demonstrated moderate discrimination in hospitalized patients with CAP. Although PNI alone did not significantly outperform PSI or CURB-65, adding PNI significantly improved the discriminatory performance of both established severity scores, supporting its potential incremental prognostic value.