BASE: Bronchiectasis Severity and Exacerbation Risk Study (BASE)

Non-cystic fibrosis bronchiectasis (NCFB) is a chronic airway disease characterized by permanent bronchial dilatation, impaired mucociliary clearance, recurrent infection, persistent airway inflammation, and repeated exacerbations. Disease severity and future exacerbation risk are heterogeneous among patients, and accurate baseline risk stratification remains clinically important for follow-up planning, preventive strategies, and early identification of patients at higher risk of clinical deterioration.

Existing bronchiectasis severity tools provide useful clinical stratification, but several established approaches include variables such as previous exacerbation history, previous hospitalization, subjective dyspnea assessment, or culture-based microbiological classification. These variables may be influenced by health-care access, documentation quality, patient perception, physician decision thresholds, sputum sampling quality, timing of culture, and prior antibiotic exposure. Therefore, there is a need to evaluate whether a focused objective disease-signature framework can classify current disease severity and predict future exacerbation risk using baseline functional, radiological, oxygenation, and inflammatory variables.

The Bronchiectasis Assessment of Severity and Exacerbations (BASE) framework is designed as a baseline clinical assessment model for adults with non-cystic fibrosis bronchiectasis (NCFB). The framework includes two linked baseline models: the BASE Severity model (BASE-S) for current bronchiectasis severity classification and the BASE Prognostic model (BASE-P) for prediction of 12-month bronchiectasis exacerbation risk. Detailed variable definitions, scoring rules, point-conversion methods, endpoint hierarchy, development-validation governance, and analytic specifications are archived in a restricted-access Zenodo record before final model derivation and validation: https://doi.org/10.5281/zenodo.20143505

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This is a prospective observational cohort study. Participants will not be assigned to any treatment or intervention by the study protocol. All clinical management decisions, including airway clearance, antibiotic treatment, inhaled therapy, microbiological testing, follow-up frequency, and hospitalization decisions, will follow routine clinical care and institutional practice.

Eligible participants will undergo baseline clinical assessment, pulmonary function assessment, chest imaging review, resting room-air oxygenation assessment, and inflammatory marker assessment. Follow-up will continue for 12 months. During follow-up, bronchiectasis exacerbations, severe exacerbations requiring hospitalization, lung-function change, inflammatory marker change, treatment escalation, and clinical outcomes will be recorded using structured data collection forms.

The study will use a development-validation design. The BASE-S and BASE-P equations, point structures, severity categories, and risk bands will be derived in the development cohort. The final locked models will then be applied unchanged to the validation cohort. No refitting, recalibration, variable substitution, point-score modification, or threshold retuning will be performed in the validation cohort. Model performance will be assessed using discrimination, calibration, risk-band separation, clinical utility where applicable, and comparison with established bronchiectasis severity tools where complete data are available.

The intended output is a practical baseline disease-signature framework that can support severity classification and one-year exacerbation-risk prediction in adults with non-cystic fibrosis bronchiectasis (NCFB), while preserving separation from any future interventional treatment studies.