Usefulness of soluble interleukin 2 receptor in differentiating tuberculous and carcinomatous pleural effusions

To evaluate the usefulness of soluble interleukin 2 receptor (sIL-2R) in differentiating tuberculous and carcinomatous pleural effusions.

Levels of sIL-2R were measured simultaneously in plasma and pleural fluid in 111 patients with pleural effusions of unknown causes.

The causes of pleural effusions were tuberculosis in 42 cases, carcinoma in 41 cases, pneumonia in 18 cases, and heart failure in 10 cases. In all groups of patients, sIL-2R levels were significantly higher in pleural fluid than in plasma. Plasma and effusion levels of sIL-2R were highest in the patients with tuberculosis, followed by those with carcinoma, pneumonia, and heart failure. Levels were significantly higher in the tuberculous group than in the carcinomatous group. To differentiate tuberculous from carcinomatous effusions, the highest plasma and effusion sIL-2R values obtained from the carcinomatous group were chosen as cutoff points (test specificity, 100%). The sensitivities of plasma and effusion sIL-2R levels in differentiating tuberculous and carcinomatous pleural effusions were 50% (21 of 42 samples) and 81% (34 of 42 samples), respectively.

Although increased plasma and pleural fluid levels of sIL-2R should not be viewed as a diagnostic test specific for tuberculous pleural effusion, sIL-2R level appears to be clinically useful as a biochemical marker to differentiate tuberculous and carcinomatous pleural effusions.