Abstract
BACKGROUND: Severity of community-acquired pneumonia (CAP) depends on microbial pathogenicity, load and virulence, and immune responses. The Infectious Disease Society of America and the American Thoracic Society (IDSA/ATS) minor criteria responsible for clinical triage of patients with CAP are of unequal weight in predicting mortality. It is unclear whether the IDSA/ATS major/minor criteria might be strongly and positively associated with the immune responses. It is warranted to explore this intriguing hypothesis. METHODS: A prospective cohort study of 404 CAP patients was performed. Cold-inducible RNA-binding protein (CIRP) levels were measured using a sandwich-based enzyme-linked immunosorbent assay. The receiver operating characteristic curves were created and the areas under the curves were calculated to illustrate and compare the accuracy of the indices. RESULTS: Severe CAP patients meeting the major criteria had the highest plasma concentrations of CIRP. The more the number of most predictive minor criteria strongly associated to mortality, i.e. arterial oxygen pressure/fraction inspired oxygen ≤ 250 mmHg, confusion, and uremia, present, the higher the CIRP level. Interestingly, the patients with non-severe CAP meeting the most predictive minor criteria demonstrated unexpectedly higher CIRP level compared with the patients with severe CAP not fulfilling the criteria. Procalcitonin (PCT), interleukin-6 (IL-6), C-reactive protein (CRP), sequential organ failure assessment (SOFA) and pneumonia severity index (PSI) scores, and mortality confirmed similar intriguing patterns. CIRP was strongly linked to PCT, IL-6, CRP, minor criteria, SOFA and PSI scores, and mortality (increased odds ratio 3.433). The pattern of sensitivity, specificity, positive predictive value, and Youden's index of CIRP ≥ 3.50 ng/mL for predicting mortality was the optimal. The area under the receiver operating characteristic curve of CIRP was the highest among the indices. CONCLUSIONS: CIRP levels were strongly correlated with the IDSA/ATS major/minor criteria. CIRP might determine the severity and the presences of major/minor criteria and best predicted mortality, and a CIRP of ≥ 3.50 ng/mL might be more valuable cut-off value for severe CAP, suggesting that CIRP might be a novel and intriguing biomarker for pneumonia to monitor host response and predict mortality, which might have implications for more accurate clinical triage decisions.