COMBINED USE OF PLEURAL ADENOSINE-DEAMINASE WITH LYMPHOCYTE NEUTROPHIL RATIO - INCREASED SPECIFICITY FOR THE DIAGNOSIS OF TUBERCULOUS PLEURITIS/

Increased pleural fluid adenosine deaminase (ADA) activity is classica lly associated with tuberculous pleuritis. However, increased activity can also occur in a number of other diseases and this may negatively affect the diagnostic utility of ADA measurements and decrease its spe cificity for the diagnosis of tuberculosis (TB). The presence of ADA i n pleural fluids reflects the cellular immune response in the pleural cavity and in particularly, the activation of T lymphocytes. Different disease entities are typically associated with the presence of partic ular types of leukocytes. Objective: To determine whether the combined use of ADA activity and differential cell counts would provide a more efficient means for diagnosing tuberculous pleurisy than the use of A DA levels alone. Methods: Biochemistry, cytology, and microbiology stu dies were performed on 472 consecutive pleural fluids. ADA and differe ntial cell counts were determined on all exudative effusions. Results: ADA activity in tuberculous effusions was significantly higher than i n any other diagnostic group (p<0.005). At a level of 50 U/L, the sens itivity, specificity, positive predictive value (ppv), negative predic tive value (npv), and efficiency for the identification of TB were cal culated at 91%, 81%, 84%, 89%, and 86%, respectively. When the additio nal requirement of a lymphocyte neutrophil ratio of 0.75 or greater wa s included, the sensitivity, specificity, ppv, npv, and efficiency for the identification of TB were calculated at 88%, 95%, 95%, 88%, and 9 2%, respectively. Conclusion: ADA, especially when combined with diffe rential cell counts and lymphocyte/neutrophil ratios, remains a useful test in the diagnosis tuberculous pleuritis.