Neutrophil elastase as a biomarker for bacterial infection in COPD

BackgroundChronic obstructive pulmonary disease (COPD) is predominantly associated with neutrophilic inflammation. Active neutrophil elastase (NE) is a serine proteinase, secreted by neutrophils, in response to inflammation and pathogen invasion. We sought to investigate if NE could be used as a biomarker for bacterial infection in patients with COPD.MethodsNE was quantified using ProteaseTag (R) Active NE Immunoassay (ProAxsis, Belfast) from the sputum of COPD subjects at stable state, exacerbation and 2weeks post treatment visit.ResultsNE was measured in 90 samples from 30 COPD subjects (18 males) with a mean (range) age of 65 (45-81) years and mean (SD) FEV1 of 47% (18). The geometric mean (95%CI) of NE at stable state was 2454ng/mL (1460 to 4125ng/mL). There was a significant increase in NE levels at an exacerbation (p=0.003), and NE levels were higher in a bacterial-associated exacerbation (NE log difference 3.873, 95% CI of log difference 1.396 to 10.740, p=0.011). NE was an accurate predictor of a bacteria-associated exacerbation (area (95%CI) under the receiver operator characteristic curve 0.812 (0.657 to 0.968).ConclusionNE is elevated during exacerbations of COPD. NE may be a viable biomarker for distinguishing a bacterial exacerbation in patients with COPD.Trial registrationLeicestershire, Northamptonshire and Rutland ethics committee (reference number: 07/H0406/157).