Cells in pleural fluid. Their value in differential diagnosis.

Pleural fluids from 182 patients were studied prospectively. Although red blood cell (RBC) counts of greater than 10,000/cu mm were common with all types of effusions, an RBC count greater than 100,000/cu mm strongly suggested malignant neoplasm, pulmonary infarction, or trauma. Of 31 exudative effusions with a lymphocytic predominance, 30 were due either to tuberculosis or neoplasm. No tuberculous effusions had more than 1% mesothelial cells, while most other effusions contained at least 5% mesothelial cells. Pleural fluid cytological studies showed malignant cells in 33 of 43 patients with effusions due to tumor. More than 50% of the effusions with originally inconclusive pleural fluid cytological findings were proved to be due to neoplasm. When tumor is suspected, at least three separate pleural fluid specimens should be submitted for cytological examination.