Authors: Raseel B. Almutairi , Nada R. Al-khater , Hoor J. Alalwan , Saadaldean S. Alsharif , Ali J. Alkhazal , Omar M. Alzuabi , Mohammed A. Almulla , Abdulellah S. AlGhamdi , Aljory J. AlBasheeri , Ryan A. Alharbi , Sulaiman M. Alanazi , Eiman M. AlShammari

Abstract

Community-acquired pneumonia (CAP) remains the primary cause of infectious mortality worldwide. Bedside severity scores (CURB-65 (confusion, urea, respiratory rate, blood pressure, age ≥65) and the Pneumonia Severity Index [PSI]) provide static triage risk but lack dynamic sensitivity to progressive clinical deterioration. We synthesized evidence on the prognostic accuracy of the neutrophil-to-lymphocyte ratio (NLR) across adult CAP cohorts. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines, four databases were searched for adult CAP cohorts reporting NLR-associated outcomes. Area under the curve (AUC) values were descriptively summarized across heterogeneous thresholds, and a random-effects meta-analysis of complete dichotomous mortality data was performed with pre-specified sensitivity analyses. A total of 19 adult cohorts (N = 19,188) were included. Across 14 studies reporting discriminative accuracy, NLR demonstrated moderate prognostic discrimination (descriptive mean AUC 0.736 ± 0.107, range 0.570-0.940). Across the 12 composite models, adding NLR yielded a descriptive mean AUC gain of +0.071, with a greater
enhancement for simpler bedside scores. Serial monitoring (days 3-5 vs. 1) distinguished survivors (declining NLR) from nonsurvivors (rising NLR). Across eight cohorts with dichotomous mortality data, elevated NLR was associated with increased mortality (random-effects risk ratio [RR] = 3.92, 95% confidence interval [CI]: 2.23-6.88; I² = 89.8%); sensitivity analysis excluding a zero-event outlier yielded RR = 3.48 (95% CI: 2.01-6.02; I² = 90.1%), while fixed-effect pooling yielded RR = 2.01 (95% CI: 1.78-2.28). NLR provides moderate prognostic discrimination in adult patients with CAP. Its principal clinical value is as an early serial marker and adjunctive
tool alongside CURB-65/PSI, not a standalone replacement.

Keywords: Neutrophil-to-lymphocyte ratio, community-acquired pneumonia, prognostic biomarker, mortality, severity score, meta-analysis.