Clinical outcome of mild to very-mild asthma with high sputum eosinophils: a prospective longitudinal study.

<bold>Background:</bold> Only a small proportion of patients with very mild to mild asthma will develop a more severe form of the disease. High eosinophils appear to be predictors of poorer short-term outcomes in mild asthma, but data are needed on patients who experience an increase in disease severity. <bold>Aim:</bold> To compare evolution of very mild and mild asthmatics showing high (≥3% S-EOS) vs low (<3% S-EOS) baseline sputum eosinophils. <bold>Methods:</bold> This longitudinal multicenter study included 2 visits >12 months apart. Adults with very mild or mild asthma and a previous sputum differential cell count result identified through local databases were asked to come back for a follow-up visit. Annual decline in forced expiratory volume in one second (FEV₁) and change in asthma medication between visits were compared between groups. <bold>Results:</bold> We included 66 subjects (41 females (64%), mean age 34 years) of whom 26 (39%) had ≥3% S-EOS. The mean time between visits was 10.3 years. Groups were similar for demographics and clinical data, except for a lower PC₂₀ in the ≥3% S-EOS group (1.65 (0.72-2.58) mg/mL vs 3.85 (2.37-5.30) mg/mL, P=0.02). Although decline in FEV₁ was similar (≥3% S-EOS: -0.52 (−2.45-1.41) mL/year vs <3% S-EOS: -0.46 (−1.94-1.01) mL/year, P=0.63), more subjects in the ≥3% S-EOS group tended to show such decline (77% vs 50%, P=0.08). Moreover, a higher proportion of subjects with ≥3% S-EOS evolved to a more severe disease based on ICS doses requirement (46% vs 14%, P=0.03). <bold>Conclusions:</bold> Using available clinical characteristics, clinicians still face challenges to identify who will evolve to a more severe form of asthma. Use of S-EOS could help identify patients at risk of poorer evolution.