Blood eosinophilia as a predictor of acute exacerbation in fibrotic interstitial lung diseases.

Fibrotic interstitial lung disease (fILD) is a heterogeneous group of rare diseases with a poor prognosis. Given the pro-fibrotic effects of eosinophils, we aimed to assess the distribution of blood eosinophil count (BEC) in patients with fILD and to investigate its potential association with outcomes. Single-center retrospective study of patients diagnosed with fILD between January 1, 2017 and December 31, 2022. For each patient, BECs during follow-up (except for those sampled during treatment with high-dose glucocorticoids) were pooled to assign a unique number (median). Patients' characteristics were analysed by BEC (Eo-high and Eo-low subgroups corresponding to BEC ≥75th percentile and <75th percentile, respectively). Predictors of outcomes were assessed by multivariate logistic regression. 201 patients were included. BEC's median and 75th percentile were 0.2 × 109/L and 0.3 × 109/L, respectively. Baseline BEC and median BEC during follow-up were strongly correlated (r1 = 0.66, 95 % IC 0.52-0.78, p < 0.001). Eo-high patients were significantly older (73 vs. 67 years, p = 0.014) and more likely to experience AE-ILD (36 % vs. 15 %, p = 0.002). In multivariate analysis, a diagnosis of IPF (OR 2.62, 95 % IC 1.05-7.02, p = 0.05), idiopathic NSIP (OR 3.69, 95 % IC 0.99-13.74, p = 0.05), baseline supplemental oxygen therapy (OR 4.71, 95 % IC 2.09-10.82, p < 0.001) and median BEC ≥0.3 × 109/L (OR 2.76, 95 % IC 1.25-6.14, p = 0.01) were associated with AE-ILD. BEC can be associated with AE-ILD. These findings pave the way for future research regarding the role of eosinophils in fILD.