Comparison of different techniques to evaluate active neutrophil elastase in sputum of bronchiectasis and cystic fibrosis patients

Neutrophil elastase (NE) is a crucial marker of neutrophilic inflammation in bronchiectasis (BE) and cystic fibrosis (CF). We aimed at comparing different techniques to detect active NE in sputum samples of 50 BE and 50 CF adults recruited during stable state at the Bronchiectasis and CF Programs of the Policlinico Hospital in Milan, Italy. Three methods including a ProteaseTag® Active NE Immunoassay (ELISA) and two enzymatic digestion assays (chromogenic –CS- and fluorogenic –FS- substrate) were compared. Results of active NE were also correlated with different clinical data. The three methods provided statistically different values for NE activity in the same sputum samples in both cohorts. The three methods were comparable in terms of consistency and agreement. In the BE cohort, the highest correlation between NE activity and Bronchiectasis Severity Index (rho=0.40, P