Increased Neutrophil Elastase in Affected Lobes of Bronchiectasis and Correlation of Its Levels between Sputum and Bronchial Lavage Fluid

Background: Neutrophil elastase (NE) has been proposed as a potential biomarker for evaluating the severity and prognosis of bronchiectasis. This study aimed to compare bronchial lavage quantification of NE levels and activities with those of sputum. Methods: A cross-sectional study was conducted in which 24 Vietnamese adults with bronchiectasis were enrolled from June 2023 to August 2023. All participants underwent bronchoscopy to collect bronchial lavage fluid (BLF) from two bronchial locations: one in the region with the greatest bronchial dilatation and one in the normal bronchi or in patients with all lobes affected, the least abnormal lobe (abnormal BLF [ABLF] and normal BLF [NBLF], respectively). Spontaneously expectorated sputum was also collected. Results: Out of 24 cases, the prevalence of mild, moderate and severe bronchiectasis was 14/24 (58.4%), 5/24 (20.8%), and 5/24 (20.8%), respectively. NE concentration and activity were significantly higher in sputum and ABLF than in NBLF (p<0.001). Sputum and ABLF were highly correlated (r=0.841, p<0.001) with no significant difference in NE activity between sputum and ABLF. Higher levels of NE activity were seen in more severe bronchiectasis than in mild bronchiectasis in all samples but were only statistically significant for NE activity in sputum (r=0.418, p=0.042). Conclusion: NE activity and concentration are elevated in areas of the lung most affected by bronchiectasis. Sputum is a valid surrogate of pulmonary NE levels, as they correlate strongly with ABLF and confirm in a Vietnamese population the relationship between NE activity and disease severity.