Abnormal type or counts of nucleated immune cells and acellular components in bronchoalveolar lavage (BAL) fluid. BAL us performed with a fiberoptic bronchoscope in the wedged position within a selected bronchopulmonary segment. BAL is commonly used to inform the differential diagnosis of interstitial lung disease or to monitor therapeutic interventions. [https://orcid.org/0000-0003-0113-912X]