Autoantibody Positivity in Bronchiectasis Without Interstitial Lung Diseases: Risk Factors and Impact on Clinical...

Objective: To characterise circulating autoantibodies, identify associated risk factors, and evaluate their impact on clinical features in bronchiectasis (BR) patients without interstitial lung diseases (ILDs). Methods: This retrospective observational study analysed 506 non-ILD BR inpatients, categorised into isolated BR (n = 240), autoantibody (AAb)-positive BR (n = 131), and connective tissue disease (CTD)-BR (n = 135) groups. Clinical features were compared, and multinomial logistic regression was used to identify factors associated with AAb positivity and CTD. Results: Compared with isolated BR, older age (OR 1.062, 95% CI 1.022-1.103, p = 0.002) and prior PTB (OR 3.481, 95% CI 1.239-9.779, p = 0.018) were independently associated with AAb-positive BR, while CTD-BR was further associated with female sex (OR 2.677, 95% CI 1.021-5.586, p = 0.046) and greater lower-lobe involvement (OR 4.115, 95% CI 1.947-13.672, p = 0.015). A significantly higher frequency of Pseudomonas aeruginosa in the lower respiratory tract was observed in RA (rheumatoid arthritis)-BR compared to isolated BR, AAb-positive BR, and other CTD-BR (43.4% vs. 22.2%, 25.2%, and 18.2%, p = 0.002). This association remained significant after adjusting for confounders (OR 4.386, 95% CI 1.729-15.328, p = 0.007). Conclusions: In non-ILD BR patients, AAb positivity presented limited clinical differences compared with isolated BR, with older age and prior PTB independently associated, possibly reflecting underlying immune dysregulation. RA-BR showed a potential independent association with P. aeruginosa isolation, warranting further investigation.