Diagnostic Value of Total and Differential Leukocyte Counts in Pleural Effusions

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Abstract
Total and differential leukocyte counts in pleural fluid were determined prospectively in 140 consecutive patients undergoing diagnostic thoracentesis. The total number of leukocytes was higher in exudates than in transudates. Lymphocytes predominated overwhelmingly (80% of all leukocytes) in 29 of the 31 effusions with verified or probable tuberculous etiology and in 18 of the 24 with malignant etiology and in 20 exudative pleural effusions of other causes. The significant differences in the percentage of lymphocytes distinguished tuberculous effusions from parapneumonic (P < 0.001), nonspecific (P < 0.001) and rheumatoid effusions (P < 0.005), and from effusions caused by undefined connective tissue disease (P < 0.001). Eosinophilia (10%) of the pleural fluid was not present in any patient with proven tuberculosis and in only 1 patient with malignant effusion (malignant mesothelioma) but did occur in 12 of the 26 patients with nonspecific effusion. A great lymphocytic predominance is characteristic particularly of tuberculous but also of malignant pleural effusions, although this predominance cannot be regarded as disease-specific. Eosinophilia of the pleural fluid, usually a nonspecific sign, indicates nontuberculous, nonmalignant etiology.