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. Methods Sputum samples from 142 COPD patients (102 men) with a mean (range) age 69 years (45 to 85) and mean (SD) post-bronchodilator percentage predicted FEV1 of 50% (19) were analysed 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 50.5ng/mL (41.4 to 61.7). PTX3 levels correlated with absolute neutrophil count in sputum (r=0.37; p<0.01); but not FEV1 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 colonisation (defined as >105 CFU/mL at stable state) with a receiver operator characteristic (ROC) area under the curve (AUC) of 0.59, 95% confidence interval (CI) 0.43 to 0.76, p=0.21). During an exacerbation there was a modest increase in PTX3 (fold difference 0.15, 95% of difference 0.02 to 0.29; p=0.02 and PTX3 fared better at identifying a bacteria-associated exacerbation (ROC AUC 0.65, 95%CI 0.52 to 0.78, p=0.03). Conclusions 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.