Protocol for the INterstitial lung Disease EXacerbations (INDEX) Study: a retrospective multicentre cohort study

Hospitalisation for respiratory-related events is an important contributor to morbidity and mortality in individuals with fibrotic interstitial lung disease (fILD). Many such hospitalisations are due to acute exacerbations (AE-fILD), but AEs are poorly understood and there are limited evidence-based guidelines for their management. Most research in this area focuses on AEs of idiopathic pulmonary fibrosis (IPF), the commonest fILD and AEs of non-IPF fILD are less well studied. Furthermore, patients with fILD who are hospitalised with a respiratory-related event but do not meet the diagnostic criteria for AE are an important under-studied group. The INterstitial lung Disease EXacerbations (INDEX) study will describe in detail a large real-world population with fILD admitted to hospital for respiratory-related causes, including AE-fILD, as well as identify potential prognostic factors.

This multicentre retrospective cohort study will analyse case notes for patients admitted to hospital between 1 September 2022 and 31 August 2023. Patient demographic data, clinical features on hospital admission, pre and postadmission investigation results, treatment approaches taken and mortality data will be collected. These data will be used to describe the patient population and to identify associations between patient, clinical presentation and treatment factors and outcomes. The primary outcome will be transplant-free survival at 90 days following the commencement of the index admission.

The study has been approved by the Health Research Authority (HRA) (IRAS 317419) and has been prospectively registered on clinicaltrials.gov (NCT06685874). The HRA waivered the requirement for Research Ethics Committee approval due to only anonymised routinely collected clinical data being collected.

This study will enhance our understanding of respiratory-related hospital admissions in fILD, including AE-fILD. The resulting data will describe a real-world patient population, define current standard care and may indicate prognostic and treatment factors to be assessed in future clinical trials.