Systemic inflammatory indices and 28-day mortality in severe pneumonia: a retrospective single-center exploratory study

Background: Severe pneumonia remains a major cause of intensive care unit admission and death, and practical tools for early risk stratification remain limited. We evaluated several readily available systemic inflammatory indices and their association with 28-day all-cause mortality in patients with severe pneumonia. Methods: = 63). Systemic immune-inflammation index (SII), systemic inflammatory response index (SIRI), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and inflammatory burden index (IBI) were calculated from routine laboratory data. Logistic regression models with progressive adjustment were used to evaluate the independent associations of these indices with 28-day mortality. Results: Several inflammatory indices were higher in patients who died within 28 days. In unadjusted and minimally adjusted analyses, SIRI, NLR, and IBI were significantly associated with 28-day mortality. After further adjustment for age, sex, body mass index, smoking, drinking, admission APACHE II score, oxygenation index, mechanical ventilation duration, and major baseline comorbidities, only SIRI and NLR remained independently associated with 28-day mortality. In the fully adjusted model, each 1-standard deviation increase in SIRI and NLR was associated with higher odds of 28-day death (SIRI: OR 2.16, 95% CI 1.08-4.33; NLR: OR 2.12, 95% CI 1.14-3.95). By contrast, the associations of SII and IBI were attenuated after additional adjustment, and PLR was not independently associated with 28-day mortality. Conclusion: Among the evaluated inflammatory indices, SIRI and NLR showed the most stable independent associations with 28-day all-cause mortality in severe pneumonia. These findings are exploratory and require external validation, but they suggest that selected inflammation-based indices may provide additional prognostic information beyond conventional severity markers.