Patterns of bronchoalveolar lavage in fibrotic and non-fibrotic interstitial lung diseases – a multicenter analysis

BACKGROUND: Bronchoalveolar lavage (BAL) cellular analysis is recommended as part of the diagnostic workup of interstitial lung diseases (ILD) when diagnosis is unclear. In recent years, ILD have been classified based on the presence or absence of fibrosis. The objective of this study was to compare BAL cellular profiles across multiple ILDs, stratified by fibrosis status. METHODS: A retrospective multicenter study of consecutive patients who underwent bronchoscopy, including BAL for ILD evaluation, between 2017 and 2022. BAL indices were chosen based on guidelines and prior research. Chest radiologists blinded to clinical data performed radiological assessment. ILD diagnoses were assigned by multi-disciplinary discussion. RESULTS: In total, 238 patients with BAL results were included (mean age 60 years, 46% females, 50.4% with fibrotic ILD, 91% with concurrent transbronchial biopsy). BAL lymphocytes > 20% and > 30% were more prevalent in non-fibrotic compared to fibrotic ILD (36.4% vs. 17.5% and 25.4% vs. 9.2%, p < 0.01). In multivariate linear regression model, fibrotic disease was associated with lower lymphocyte counts (β=-6.15, p = 0.007). Rates of mixed BAL pattern, lymphocytosis, or isolated neutrophils > 3% did not distinguish between fibrotic diseases. On computed tomography, BAL lymphocytosis was not associated with ground-glass opacities or mosaic attenuation in both fibrotic and non-fibrotic groups, while honeycombing was associated with a lower rate of elevated (> 4.5%) BAL neutrophils (71% vs. 91%, p = 0.018). CONCLUSION: Specific patterns in BAL differential were uncommon in fibrotic ILD and were not different among its subtypes. As a stand-alone modality, BAL seems to have a limited utility in fibrotic ILD.