Rationale: Blood eosinophil count predicts response to inhaled corticosteroids and specific biologic therapies in selected patients with asthma. Despite this important role, fundamental aspects of eosinophil behavior in asthma have not been studied. Objectives: To investigate the behavior of blood eosinophils in a population, comparing their distribution with the general population and studying their intraindividual variability over time in relation to hospital episodes (emergency department visits and hospitalizations) in clinical practice. Methods: The distribution and variability of 35,703 eosinophil determinations in 10,059 stable patients with asthma were investigated in the MAJORICA (Majorca Real-Life Investigation in COPD and Asthma) cohort. Eosinophil distribution in the asthma population was compared with a control sample from the general population of 8,557 individuals. Eosinophil variability and hospital episodes were analyzed using correlations, receiver operating characteristic (ROC) curves, and multiple regression analysis. We defined the Eosinophil Variability Index as (Eosmax - Eosmin / Eosmax) × 100%. The findings of the asthma population were retested in an external well-characterized asthma cohort. Results: The eosinophil count values and variability were higher in the asthma population than in the general population (P < 0.001). Variability data showed a better association with hospital episodes than the counting values. An Eosinophil Variability Index ⩾50% was a better predictor for any hospital episode than any of the absolute counting values. These results were validated in the external cohort. Conclusions: The eosinophil variability in patients with asthma better identifies the risk of any hospital episode than the absolute counting values currently used to target specific treatments.
Keywords: asthma; eosinophil; health resources; variability.