Blood eosinophilia: a predictive marker of acute exacerbations in fibrotic interstitial lung disease?

<bold>Background:</bold> Interstitial lung disease (ILD) is a heterogeneous group of rare diseases with a poor prognosis. Reliable biomarkers are lacking for their management. Considering the pro-fibrotic effects of eosinophils, we hypothesized that blood eosinophilia could be a treatable trait in fibrotic ILD (fILD). The aim of this study was to investigate the association between blood eosinophilia and fILD’s outcomes. <bold>Methods:</bold> We conducted a single-centre retrospective study to assess the association between blood eosinophil count (BEC) in patients with fILD and the occurrence of death, transplantation, acute exacerbation, or progression of fibrosis. Multivariate logistic regression was used to identify patient characteristics associated with a high BEC (≥ 75th percentile in our population). <bold>Results:</bold> 201 patients with fILD were included. The median BEC was 0.2 G/L and the 75th percentile threshold was 0.3 G/L. Median BEC was significantly higher in patients with acute exacerbation of ILD (AE-ILD) during follow-up (p=0.0013) or with progressive pulmonary fibrosis (PPF) (p=0.0074). After adjustment, median BEC ≥ 0.3 G/L was statistically associated with the occurrence of exacerbations (OR=2.65, 95% CI=1.25-5.59, p=0.01). These results were similar when considering the BEC at time of diagnosis. <bold>Conclusion:</bold> Median BEC during follow-up and BEC at diagnosis were statistically associated with the occurrence of AE-ILD as well as with PPF, independent of the diagnosis of underlying fILD.