The bronchiectasis severity index. An international derivation and validation study

Abstract

Rationale: There are no risk stratification tools for morbidity and mortality in bronchiectasis. Identifying patients at risk of exacerbations, hospital admissions, and mortality is vital for future research.

Objectives: This study describes the derivation and validation of the Bronchiectasis Severity Index (BSI).

Methods: Derivation of the BSI used data from a prospective cohort study (Edinburgh, UK, 2008-2012) enrolling 608 patients. Cox proportional hazard regression was used to identify independent predictors of mortality and hospitalization over 4-year follow-up. The score was validated in independent cohorts from Dundee, UK (n = 218); Leuven, Belgium (n = 253); Monza, Italy (n = 105); and Newcastle, UK (n = 126).

Measurements and main results: Independent predictors of future hospitalization were prior hospital admissions, Medical Research Council dyspnea score greater than or equal to 4, FEV1 < 30% predicted, Pseudomonas aeruginosa colonization, colonization with other pathogenic organisms, and three or more lobes involved on high-resolution computed tomography. Independent predictors of mortality were older age, low FEV1, lower body mass index, prior hospitalization, and three or more exacerbations in the year before the study. The derived BSI predicted mortality and hospitalization: area under the receiver operator characteristic curve (AUC) 0.80 (95% confidence interval, 0.74-0.86) for mortality and AUC 0.88 (95% confidence interval, 0.84-0.91) for hospitalization, respectively. There was a clear difference in exacerbation frequency and quality of life using the St. George's Respiratory Questionnaire between patients classified as low, intermediate, and high risk by the score (P < 0.0001 for all comparisons). In the validation cohorts, the AUC for mortality ranged from 0.81 to 0.84 and for hospitalization from 0.80 to 0.88.

Conclusions: The BSI is a useful clinical predictive tool that identifies patients at risk of future mortality, hospitalization, and exacerbations across healthcare systems.

Figure 1.

The performance of the Bronchiectasis Severity Index in predicting mortality, hospital admissions, exacerbations, and quality of life. All between-group comparisons were statistically significant (P < 0.0001). The exacerbation and quality-of-life data are presented as mean with SD. AUC = area under the receiver operator characteristic curve.

Figure 2.

Validation of the Bronchiectasis Severity Index (BSI) in external cohorts. (A) Mortality and hospital admissions according to mild (0–4 points), moderate (5–8 points), and severe (>8 points) risk BSI groups. (B) Kaplan-Meier survival curves (mortality) in the mild, moderate, and severe groups (P < 0.0001 by log rank test) in the Leuven cohort. (C) Exacerbation frequency in the mild, moderate, and severe groups according to the BSI (P < 0.0001 for Newcastle and Dundee cohorts, P = 0.03 for Monza cohort). (D) Receiver operator characteristic curves for mortality and hospital admissions according to the BSI.