Investigating the role of pentraxin 3 as a biomarker for bacterial infection in subjects with COPD

Background: Pentraxin 3 (PTX3) is an acute phase protein, involved in antibacterial resistance. Recent studies have shown PTX3 levels to be elevated in the presence of a bacterial infection and in a murine sepsis model. Objective: We aim to investigate if sputum PTX3 can be used as a biomarker for bacterial infection in subjects with COPD. Materials and methods: Sputum samples from 142 COPD patients (102 men) with a mean (range) age of 69 years (45–85) and mean (SD) post-bronchodilator percentage predicted forced expiratory volume in 1 second (FEV 1 ) of 50% (19) were analyzed for PTX3, using a commercial assay at stable state and during an exacerbation. Association with bacteria, from culture, quantitative real-time polymerase chain reaction (qPCR) and colony-forming units (CFU) was investigated. Results: The geometric mean (95% CI) PTX3 level at stable state was 50.5 ng/mL (41.4–61.7). PTX3 levels correlated with absolute neutrophil count in sputum ( r = 0.37; P , 0.01), but not FEV 1 or health status. There was a weak correlation between PTX3 and bacterial load (CFU: r = 0.29, P , 0.01; 16S qPCR: r = 0.18, P = 0.05). PTX3 was a poor predictor of bacterial colonization (defined as . 10 5 CFU/mL at stable state) with a receiver-operating characteristic (ROC) area under the curve (AUC) of 0.59 and 95% confidence interval (CI) 0.43–0.76 ( P = 0.21). During an exacerbation, there was a modest increase in PTX3 (fold difference 0.15, 95% of difference 0.02–0.29; P = 0.02), and PTX3 fared better at identifying a bacteria-associated exacerbation (ROC AUC 0.65, 95% CI 0.52–0.78, P = 0.03). Conclusion: PTX3 is associated with bacterial infection in patients with COPD, but its utility as a biomarker for identifying a bacteria-associated exacerbation warrants further studies.