 In particular, bronchoalveolar lavage is commonly used to diagnose infections in people with immune system problems, pneumonia in people on ventilators, and acute respiratory distress syndrome (ARDS).It is the most common method used to sample the epithelial lining fluid (ELF) and to determine the protein composition of the pulmonary airways.BAL has even been used therapeutically to remove mucus, improve airway ventilation, and reduce airway inflammation in conditions such as chronic obstructive pulmonary disease (COPD) and pulmonary alveolar proteinosis (PAP).