Normal cells lining the airways and alveolar spaces are encountered in exfoliative cytology specimens from the lung. The normal cell population in exfoliative cytology specimens includes ciliated columnar cells, mucous goblet cells, basal reserve cells, macrophages, and inflammatory cells. There is some variation in the cells encountered, depending on the procedure used. An essential assessment for all exfoliative pulmonary cytology specimens is whether there has been an adequate sampling. The criterion used in sputum cytology is the presence of alveolar macrophages. For bronchial brush and wash specimens, ciliated columnar cells, in addition to alveolar macrophages, should be identified for the specimen to be considered satisfactory. These same cells, including macrophages, are encountered in bronchoalveolar lavage.

Mesothelial cells are frequently encountered in exfoliative cytology specimens of pleural fluid. Generally, mesothelial cells shed into pleural effusions are considered to be reactive. The cytologic reactive changes of exfoliated mesothelial cells may be minimal, or they may be so severe as to mimic malignancy (see Chapter 130). In addition, acute and chronic inflammatory cells and red blood cells frequently appear in cytologic specimens.