Admission C-Reactive Protein for Risk Stratification in Hospitalized Adults with Community-Acquired Pneumonia: A Retrospective Cohort Study

Abstract

Background and Objectives: Admission C-reactive protein (CRP) may assist risk assessment in community-acquired pneumonia (CAP), but its prognostic value remains uncertain. Materials and Methods: In this retrospective single-center database cohort, 134 adults with records classified as CAP/pneumonia during 2019–2023 were evaluated. Admission CRP discrimination for in-hospital mortality was assessed using ROC analysis. Logistic regression was supplemented by Firth bias-reduced sensitivity analyses because only nine deaths occurred. Exploratory Spearman correlations with length of stay (LOS) were repeated among survivors. Results: Nine patients (6.7%) died. Median admission CRP was 274.4 (IQR 198.6–319.0) mg/L in non-survivors versus 126.2 (86.0–177.9) mg/L in survivors (p = 0.0045). Conventional age-adjusted logistic regression yielded an odds ratio (OR) of 5.66 per 100 mg/L CRP increase (95% CI 1.92–16.75; p = 0.0017); the Firth age-adjusted sensitivity analysis yielded OR 4.85 (95% penalized profile-likelihood CI 1.93–15.27; p < 0.001). The ROC AUC was 0.785 (bootstrap 95% CI 0.552–0.973). Among survivors, admission CRP was not significantly correlated with LOS (n = 124; Spearman ρ = 0.083; p = 0.357). Conclusions: Admission CRP remained associated with in-hospital mortality after age adjustment and penalized sensitivity analysis, but limited events, incomplete clinical characterization, and uncertainty in CAP case ascertainment constrain inference. The data-derived threshold and non-standardized serial CRP results are exploratory and require prospective validation.