Thulborn SJ, et al. - Researchers determined whether neutrophil elastase (NE) could serve as a biomarker for bacterial infection in chronic obstructive pulmonary disease (COPD) patients. Using ProteaseTag Active NE Immunoassay, they measured NE in 90 samples from 30 COPD patients. The participants, including 18 males, had a mean age of 65 (45–81) years and mean (SD) forced expiratory volume in 1 second of 47% (18). At an exacerbation, NE levels were significantly increased, and in a bacterial-associated exacerbation, NE levels were higher. Findings revealed the accuracy of NE in predicting a bacteria-related exacerbation (area (95%CI) under the receiver operator characteristic curve 0.812 (0.657 to 0.968). Elevated NE was detected during exacerbations of COPD. In patients with COPD. NE could be useful as a biomarker for differentiating a bacterial exacerbation.