Cell counts in severe asthma; concordance of sputum and BAL in Wessex Severe Asthma Cohort

Background: Asthma is widely considered an eosinophilic disease however severe asthma is frequently non-eosinophilic. Treatment options can depend on airway cell counts but proximal and distal airways may not be concordant in terms of cell differential. The Wessex Severe Asthma Cohort (WSAC) recruited 342 participants with severe asthma for detailed phenotyping with some participants undergoing sputum induction and/or bronchoscopy with bronchoalveolar lavage (BAL). We aimed to use data from the WSAC to assess the agreement between sputum and BAL cell differentials. Methods: WSAC participants with severe asthma were included if they underwent both BAL and successful sputum induction. Correlation coefficients and classification tables were used to calculate the agreement between the proximal (sputum) and distal (BAL) compartments. Results: 38 participants were included in the analysis. Correlation coefficients were 0.429 for neutrophil count (p=0.007) and 0.569 for eosinophil count (p Conclusions: Sputum and BAL cell counts showed moderate correlation, but significant classification discrepancies were found when using recognised thresholds. Sampling of multiple compartments may be required for optimal assessment of individuals with severe asthma.