Clinical implications of bronchoalveolar lavage fluid cellular analysis in fibrotic interstitial lung disease...

Although the clinical role of bronchoalveolar lavage (BAL) in interstitial lung disease (ILD) has been suggested by previous studies, its clinical utility remains debatable.

We aimed to evaluate the clinical implications of combining quantitative computed tomography (QCT) and BAL fluid cellular analysis in patients with fibrotic ILD.

This study was a retrospective, single-center study.

We analyzed patients with fibrotic ILD who underwent BAL in specific lung locations and used deep-learning-based QCT. Correlations between BAL cellular components and QCT parameters were assessed for both the whole lung and the tested lobe, and survival outcomes and disease progression were evaluated.

Among 163 patients, no significant difference was observed in BAL cellular analysis between radiologic usual interstitial pneumonia (UIP) and non-UIP groups (for all, p > 0.05). BAL neutrophil levels showed weak positive correlation with fibrosis score (whole lung: r = 0.308, p < 0.001; tested lobe: r = 0.200; p = 0.010). While BAL cellular analysis alone showed no difference in 3-year survival, a high fibrosis score (⩾20%) independently predicted 3-year mortality (hazard ratio 4.62, p = 0.002). In patients with fibrosis score ⩾10%, high BAL neutrophils (>4.5%) indicated greater 1-year fibrosis progression (log-rank test, p = 0.029). In steroid-treated patients, BAL lymphocytosis (⩾15%) was associated with a trend toward an improved prognosis (p = 0.073); however, within this group, those with fibrosis scores ⩾20% had worse outcomes in the 3-year survival rate (median survival: 16.4 months vs not reached, p = 0.039).

Although BAL fluid cellular analysis alone does not differentiate radiologic patterns or offer prognostic values, elevated BAL neutrophil levels combined with a high fibrosis score on CT may help to identify patients at higher risk of early fibrosis progression.