Bronchoalveolar lavage (BAL), also known as bronchoalveolar washing, is a diagnostic method of the lower respiratory system in which a bronchoscope is passed through the mouth or nose into an appropriate airway in the lungs, with a measured amount of fluid introduced and then collected for examination.
[9] Bronchoalveolar lavage can be a more sensitive method of detection than nasal swabs in respiratory molecular diagnostics, as has been the case with SARS-CoV-2 where bronchoalveolar lavage samples detect copies of viral RNA after negative nasal swab testing.
[3][13] It is the most common method used to sample the epithelial lining fluid (ELF) and to determine the protein composition of the pulmonary airways.
[15] A much more intense version involving up to 50 liters of fluid is called whole lung lavage (WLL) and is used to treat pulmonary alveolar proteinosis (PAP).
The physician seeks out areas with excess mucus or other abnormalities, then uses saline and suction to clean it.