Abstract
Accurate risk stratification in community-acquired pneumonia (CAP) is essential for guiding timely and effective clinical management. This study evaluated whether the combined assessment of circulating T-lymphocyte subsets (T-cell subsets) and serum procalcitonin (PCT) enhances diagnostic accuracy and severity classification in CAP. T-cell subsets, as markers of immune response, may complement traditional inflammatory biomarkers. A retrospective analysis was conducted on 320 adult CAP patients admitted to a tertiary hospital in Zhejiang, China, between February 2020 and November 2021. Patients were stratified using the Clinical Pulmonary Infection Score (CPIS ≤ 6 vs. > 6) and platelet-to-lymphocyte ratio (PLR ≤ 163 vs. > 163). Laboratory assessments included serum PCT, white blood cell count (WBC), C-reactive protein (CRP), neutrophil-to-lymphocyte ratio (NLR), interleukin-6 (IL-6), and T-cell subsets (CD3⁺, CD4⁺, CD8⁺ counts, and CD4/CD8 ratio). Pathogens were identified from 79 positive sputum or blood cultures. Patients with CPIS > 6 had significantly higher levels of PCT, PLR, WBC, CRP, NLR, and IL-6, along with lower CD3⁺ and CD4⁺ T-cell counts, a reduced CD4/CD8 ratio, and elevated CD8⁺ counts (all P < 0.05). Similar trends were observed in patients with PLR > 163. Acinetobacter baumannii was significantly more prevalent in patients classified as moderate-to-high risk or non-survivors (P < 0.05). T-cell subsets monitoring demonstrated a sensitivity of 93.2%, while PCT showed a specificity of 95.6% for predicting CAP severity. Combined evaluation of T-lymphocyte subsets and serum procalcitonin levels enhances the accuracy of CAP severity stratification. The elevated prevalence of Acinetobacter baumannii in severe cases highlights the importance of host-pathogen interactions. Integrated immune and inflammatory profiling may facilitate precision-based management strategies in CAP.