Adenosine deaminase levels in nontuberculous lymphocytic pleural effusions

Objectives: Adenosine deaminase (ADA) can aid in the diagnosis of tuberculo us pleural effusions, but false-positive findings from lymphocytic, effusio ns have been reported. We studied the ADA levels in a variety of nontubercu lous lymphocytic effusions and analyzed the relationships between ADA and c onventional hematologic and biochemical parameters. Methods: One hundred six lymphocytic pleural fluid samples (lymphocyte coun t > 50%) were analyzed. These included post-coronary artery bypass grafting (CABG) effusions (n = 45), malignant effusions (n = 27), miscellaneous exu dative effusions (n = 10), and transudative effusions (n = 24). ADA levels were determined using the Giusti method. In 22 randomly selected cases, ADA was measured again on the same sample 6 weeks later. Results: The ADA level reached the diagnostic cutoff for tuberculosis (40 U /L) in only three cases (2.8%): two lymphomas and one complicated parapneum onic effusion. There was no significant correlation between effusion ADA le vels and the total leukocyte (r = 0.08), differential lymphocyte (r = 0.18) or monocyte (r = - 0.18) counts. ADA levels were significantly lower in th e transudative effusions (7.2 +/- 3.5 U/L) than in post-CABG (16.6 +/- 7.2 U/L), malignant (15.3 +/- 11.2 U/L), and other exudative (15.4 +/- 13.1 U/L ) effusions (p < 0.001). ADA measurements were consistent when assayed 6 we eks apart (r = 0.95; p < 0.00001; coefficient of variation, 14%). Conclusions: ADA levels in nontuberculous lymphocytic effusions seldom exce eded the diagnostic cutoff for TB. Effusion ADA levels cannot be predicted from total or differential leukocyte counts. Post-CA-BG pleural fluids had ADA levels similar to other nontuberculous lymphocytic effusions. ADA is st able in effusion fluids, and its measurement is reproducible.