Background: Sputum rheology is increasingly being used in chronic respiratory diseases with the view to further understand the role of mucus and help with management. The rheology critical stress value measures the force needed for the sputum to flow and is believed to be linked with airway clearance ability, and may therefore be related to asthma symptoms and control.

Aim: To assess the relation between sputum rheology and asthma control in patients with suppressed airway eosinophils on benralizumab.

Methods: Sputum rheology and differential cell count were performed on 20 spontaneous sputum samples from patients with associated clinical data (steroid requirement, inflammatory markers, asthma control questionnaire (ACQ6) and quality of life).

Results: Most patients (90%) on benralizumab had sputum eosinophils <3%. Patients were divided in groups according to their critical stress levels (low stress <20 Pa and high stress >20 Pa). ACQ6 was statistically lower in the patients with lower critical stress (low stress group median (Q1-Q3) 1.49(0.16-2.16), high stress group 3.50(2.50-4.00), p <0.01) (Figure).

Conclusions: Patients with better asthma control exhibited lower force needed for the sputum to flow from airways, independent of eosinophilic airway inflammation.

Future studies are warranted to investigate mucus behaviour, an unmet need in severe asthma.