Impact of emphysema on biomarkers in hospitalized COPD patients with community-acquired pneumonia: a retrospective study

Background Chronic obstructive pulmonary disease (COPD) is a heterogeneous disorder in which chronic bronchitis and emphysema coexist to varying degrees. Emphysema has distinct clinical and prognostic features. C-reactive protein (CRP), procalcitonin (PCT), white blood cell count (WBC), and neutrophil values are used for diagnosing community-acquired pneumonia (CAP). This study investigated whether these biomarkers differ in emphysematous patients with CAP. Methods Patients with COPD hospitalized with CAP between January 2016 and February 2023 were divided into emphysema and non-emphysema groups based on radiologic findings. Emphysema subtypes were classified, and quantitative Goddard scoring was performed. Admission demographic, clinical and laboratory data, hospital stay length and clinical outcomes (discharge, intensive care unit [ICU] transfer, in-hospital mortality) were compared between groups. CRP and PCT levels were dichotomized as low and high using predefined thresholds (CRP ≤ 200 vs. >200 mg/L; PCT < 0.10 vs. ≥0.10 µg/L). The independent effect of emphysema on low CRP and PCT levels was assessed using multivariable binary logistic regression analysis. Results Of the 135 patients included, 71 (53%) had emphysema. Median CRP and PCT levels were significantly lower in the emphysema group than in the non-emphysema group (CRP: 116, interquartile range [IQR] 56–187 vs. 254 (IQR 213-310 mg/L); p < 0.001; PCT: 0.132 [ IQR 0.079–0.536] vs. 0.356 [IQR 0.171–1.660] µg/L; p = 0.007, respectively). Median WBC and neutrophil counts were also lower ( p = 0.036; p = 0.035, respectively). In multivariable analysis, emphysema (odds ratio [OR] 54.274; 95% Confidence Interval [CI] 14.545–202.526; p < 0.001), higher glomerular filtration rate (OR 1.021; 95% CI 1.002–1.040; p = 0.026), and prior antibiotic use (OR 4.278; 95% CI 1.199–15.264; p = 0.025) were independently associated with low CRP. For low PCT, emphysema remained the only significant predictor (OR 3.694; 95% CI 1.145–11.921; p = 0.029). Length of stay was longer in emphysema (9 vs.7 days; p = 0.010), with no differences in ICU transfer or mortality. Conclusion In patients with emphysema, inflammatory biomarkers at CAP diagnosis were lower compared with those without emphysema. These findings suggest a potential difference in biomarker response; however, the retrospective design limits causality. Further prospective studies are needed to confirm these results and clarify their clinical relevance. Trial registration Not applicable. This study is a retrospective observational analysis and was not registered as a clinical trial.