Differential diagnosis of lymphocytic pleural effusion is difficult even with many laboratory findings. Nitric oxide(NO) level is higher in the sputum or exhaled breath of patients with active pulmonary tuberculosis than in those without tuberculosis. In addition, there are some reports about the increased level of NO metabolites in body fluids of cancer patients. However, there is no data on the NO levels in the pleural fluid of patients with tuberculous pleurisy.

The serum and pleural fluid NO in the patients with acute lymphocytic pleural effusion were analyzed.

Of total 27 patients, there were 14 males and average age of patients was 48 years. The final diagnosis was tuberculous pleurisy in 17 cases and malignant pleural effusion in 10. The pleural fluid NO level was 540.1±116.4 micrometerol in the tuberculous pleurisy patients and 383.7±71.0 micrometerol in the malignant pleural effusion patients. The serum NO level was 624.7±142.0 micrometerol in tuberculous pleurisy patients and 394.4±90.4 micrometerol in malignant pleural effusion patients. There was no significant difference in the serum and pleural fluid NO level between the two groups. The NO level in the pleural fluid showed a significant correlations with the pleural fluid neutrophil count, the pleural fluid/serum protein ratio, and pleural fluid/serum albumin ratio (p<0.05 in each). The protein concentration, leukocyte and lymphocyte count in the pleural fluid were significantly higher in the tuberculous pleurisy patients than the malignant pleural effusion patients (p<0.05 in each).

NO is not a suitable marker for a differential diagnosis of lymphocytic pleural effusion. However, the NO level in the pleural fluid might be associated with the neutrophil recruitment and protein leakage in the pleural space.