Determining the cause of an exudative pleural effusion is sometimes quite difficult, especially between malignant and tuberculous effusions. Twenty percent of effusions remain undiagnosed even after a complete diagnostic evaluation, including pleural biopsy. The activity of tumor necrosis factor-alpha (TNF-α), which is the one of proinflammatory cytokines, is increased in both infectious and malignant effusions. The aim of this study was to investigate the diagnostic efficiency of TNF-α activity in distinguishing tuberculous from malignant effusions.

46 patients (13 with malignant pleural effusion, 33 with tuberculous pleural effusion) with exudative pleurisy were included. TNF-α concentrations were measured in the pleural fluid and serum samples using an enzyme- linked immunosorbent assay (ELISA). In addition, TNF-α ratio (pleural fluid TNF-α : serum TNF-α) was calculated.

TNF-α concentration and TNF-α ratio in the pleural fluid were significantly higher in the tuberculous effusions than in the malignant effusions (p<0.05). However, the serum levels of TNF-α in the malignant and tuberculous pleural effusions were similar (p>0.05). The cut off points for the pleural fluid TNF-α level and TNF-α ratio were found to be 136.4 pg/mL and 6.4, respectively. The sensitivity, specificity and area under the curve were 81%, 80% and 0.82 for the pleural fluid TNF-α level (p<0.005) and 76%, 70% and 0.72 for the TNF-α ratio (p<0.05).

We conclude that pleural fluid TNF-α level and TNF-α ratio can distinguish a malignant pleural effusion from a tuberculous effusion, and can be additional markers in a differential diagnosis of tuberculous and malignant pleural effusion. The level of TNF-α in the pleural fluid could be a more efficient marker than the TNF-α ratio.