Validation of the Bronchiectasis Severity Index in alpha-1 antitrypsin deficiency

Bronchiectasis is increasingly recognised in patients with alpha-1 antitrypsin deficiency (AATD), yet prognostic tools validated in general bronchiectasis populations have not been specifically evaluated in this group. The Bronchiectasis Severity Index (BSI) is a widely used multidimensional score predicting mortality, hospitalisation, and exacerbations in all-cause bronchiectasis. This study aimed to validate the BSI in a cohort of patients with AATD-bronchiectasis. Clinical data were obtained from the Birmingham AATD registry. Patients with severe AATD genotypes and CT-confirmed bronchiectasis were included, while those with non-severe genotypes or alternative causes of bronchiectasis were excluded. BSI scores were calculated using available registry data with minor adjustments reflecting the limitations of cross-sectional data collection. Associations between BSI and mortality were assessed using Kaplan-Meier survival analysis and Cox proportional hazards models adjusted for COPD, smoking status, and sex. Secondary analyses evaluated associations between BSI and lung function decline (FEV1 and KCO) and health-related quality of life (SGRQ). A total of 198 patients were included (mean age 54.3 ± 9.7 years; 53.5% male), the majority with the ZZ genotype (97.5%) and coexisting COPD (87.4%). Median BSI score was 5 (range 0-14). Mortality differed significantly across BSI severity groups (p < 0.001): estimated 1-year mortality was 1.1%, 7.4%, and 20.0% for mild, moderate, and severe disease respectively, while 4-year mortality was 5.7%, 23.7%, and 31.8%. In Cox regression analysis adjusted for COPD, smoking, and sex, BSI remained significantly associated with mortality (hazard ratio 1.13 per point increase; 95% CI 1.05-1.23; p = 0.002). BSI score was also associated with greater decline in gas transfer (KCO) (β = -0.22% per point per year; p < 0.001), but showed no significant association with FEV1 decline or SGRQ score. The Bronchiectasis Severity Index is associated with mortality risk in patients with AATD-associated bronchiectasis, supporting its use as a prognostic tool in this population. These findings provide evidence that a severity score derived from all-cause bronchiectasis cohorts can be applied to AATD, although prospective validation in larger multicentre datasets is warranted.