Increase in Blood Eosinophil Count Over Time and Sputum IL8 are Associated with FEV₁ Decline in Asthma

Asthma is associated with accelerated rate of FEV₁ decline.

To determine predictive factors associated with accelerated FEV₁ decline in adult asthma and evaluate sputum cytokines as potential biomarkers for airflow decline.

We recruited 125 asthmatics evaluated at the asthma clinic of Liège and reevaluated them at least 5 years later. Clinical, functional and inflammatory characteristics were compared between patients with accelerated decline (FEV₁ decline > 0.85% pred.y^-1) and others. Predictive factors were highlighted with linear regression analysis. Sputum EGF, VEGF, FGF, IL5, IL8, TGF-β, and IgE levels were measured in 58 of these patients at both visits by Human XL cytokine Luminex Performance assay and Elisa.

Post-BD FEV₁ decline was 0.06 ± 2.44% pred.y^-1 in the overall population. Median (IQR) time between visits was 66 (62 - 86) months. The multivariable analysis showed that an increase in blood eosinophils over time (Δ BEC) (Reg. Coef. (95%CI): 0.002 (0.001 to 0.004), p = 0.005)) and onset of asthma (0.04 (0.003 to 0.07), p = 0.036) were independently associated with FEV₁ decline. IL8 levels measured at baseline were higher (499 (408-603) pg/ml, p = 0.0040) in patients with accelerated decline compared to others (143 (88-308) pg/ml).

In this study, we have confirmed that an increase in blood eosinophil counts over a follow-up of at least 5 years and later onset of asthma are associated with accelerated annual FEV₁ decline. Moreover, high sputum IL8 levels could be a risk factor for accelerated decline in asthma patients.