Use of pleural fluid lymphocyte neutrophil ratio in addition to pleural fluid adenosine deaminase for the diagnosis of tuberculous pleural effusion

Abstract

Increased pleural fluid adenosine deaminase (ADA) activity is classically associated with tuberculous pleuritis. However, increased activity can also occur in a number of other diseases and this may negatively affect diagnostic utility of ADA measurements and decrease its specificity for the diagnosis of tuberculosis. The presence of ADA in pleural fluid reflects cellular immune response in pleural cavity and in particular, the activation of T lymphocytes. Different disease entities are typically associated with the presence of particular type of leucocytes. The Objectives of the study was to determine whether the combined use of ADA activity and lymphocyte neutrophil ratio would provide a more efficient means for diagnosing tuberculous pleurisy than the use of ADA levels alone. Biochemistry, cytology and microbiology studies were performed on 90 consecutive pleural fluids. ADA and differential counts were determined on all exudative effusions.ADA activity in tuberculous effusions was significantly higher than in any other diagnostic group. At a level of 50U/L, the sensitivity, specificity, positive predictive value, NPV, and efficiency for identification of TB calculated at 61%, 71%, 83%, 45%, and 64% respectively. When the additional requirement of a lymphocyte neutrophil ratio of 0.75 or greater was included, the sensitivity, specificity, PPV,NPV, and efficiency for identification of TB were calculated at 100%,83%,93%,100% and 95% respectively.ADA when combined with lymphocyte neutrophil ratio remains a useful test in the diagnosis of tuberculous pleuritis.