BAL Fluid Cellular Analysis and Radiologic Patterns in Patients With Fibrotic Interstitial Lung Disease.

Background: BAL cellular analysis is often recommended during the initial diagnostic evaluation of fibrotic interstitial lung disease (ILD). Despite recommendation for its use, between-center heterogeneity exists and supportive data concerning the clinical utility and correlation of BAL findings with radiologic features or patterns remain sparse.

Research question: In patients with fibrotic ILD, are BAL findings associated with radiologic features, patterns, and clinical diagnoses?

Study design and methods: Patients with fibrotic ILD who underwent BAL for diagnostic evaluation and who were enrolled in the prospective Canadian Registry for Pulmonary Fibrosis were re-reviewed in a standardized multidisciplinary discussion (MDD). BAL was categorized according to guideline-recommended thresholds, and using thresholds of lymphocytosis > 20% and neutrophils > 4.5%. High-resolution CT (HRCT) scans were scored (anonymized to clinical data) for specific features and percentage lung involvement. Radiologists classified HRCT scans according to guideline-defined patterns for idiopathic pulmonary fibrosis and fibrotic hypersensitivity pneumonitis; then, MDD diagnoses were assigned, considering all available data.

Results: Bronchoscopy with cellular analysis was performed in 209 of 1,593 patients (13%). Lymphocyte % was weakly negatively correlated with total fibrosis % (r = -0.16, P = .023) but not statistically significantly correlated with ground glass opacity % (r = 0.01, P = .94). A mixed BAL pattern was the most frequent in all radiologic patterns (range, 45%-69%), with a minority classifiable according to BAL guidelines. BAL lymphocytosis appeared with similar frequency across HRCT patterns of fibrotic hypersensitivity pneumonitis (21%) and usual interstitial pneumonia (18%). Only 5% of patients with MDD-based fibrotic hypersensitivity pneumonitis had a guideline-defined isolated lymphocytosis > 15%.

Interpretation: BAL cellular analyses did not significantly correlate with radiologic features, guideline patterns, or MDD-based diagnoses. Ground glass opacities are often interpreted to represent pulmonary inflammation, but were not associated with BAL lymphocytosis in this cohort.