DIAGNOSTIC CUT-OFF OF PLEURAL FLUID ADENOSINE DEAMINASE (ADA) VALUE IN TUBERCULOUS PLEURAL EFFUSION

BACKGROUND Among the various aetiologies of exudative pleural effusion, tuberculosis still remains high in the list, especially in developing countries like India. Tuberculous pleural effusion is the second most common form of extrapulmonary tuberculosis, just behind lymph node tuberculosis. Establishing tuberculosis as the aetiology of pleural effusion is hence very important. Though demonstration of acid fast bacilli in pleural fluid by smear/culture or caseating granuloma in the histopathological examination of pleural biopsy are diagnostic, these are not feasible in all cases. In this context comes the diagnostic value of adenosine deaminase (ADA) in pleural fluid. This is a biochemical test done in pleural fluid, which can give a clue towards the diagnosis of tuberculous aetiology. Several studies have shown different cut-off values of ADA, above which it is considered as positive. Hence, this study was planned to find out the best cut-off value of ADA in diagnosing tuberculous pleural effusion in a tertiary care centre in Trivandrum, Kerala. The aim of this study is to determine the best cut-off value of ADA that can diagnose tuberculous pleural effusion. MATERIALS AND METHODS Settings and Design-This was a descriptive study done in the Department of Pulmonary Medicine, GMC, Trivandrum. Study population included consecutive cases of exudative pleural effusion, attending the Department during the period from January 2015 to April 2016. All exudative pleural effusions during the period were taken and a total of 175 cases (80 tuberculous) were studied. A case was taken as tuberculous using defined criteria. Patients with empyema and post-traumatic effusions were excluded from the study. Statistical Analysis-Analysis was done using SPSS version 22.0. Sensitivity and specificity of pleural fluid ADA in diagnosing tuberculosis were determined. An ROC curve was plotted to find the optimum cut-off value of ADA to predict a diagnosis of tuberculosis. This was further verified using the Youden's index. RESULTS A cut-off value of pleural fluid ADA of 38.3 U/L had a sensitivity of 93% and a specificity of 97%. Youden's index was maximum (0.89) for this value, which was taken as the optimum cut off. CONCLUSION Pleural fluid ADA levels were significantly higher in tuberculous pleural effusion when compared to the non-tuberculous group. The cut-off value of 38.3 U/L with the maximum Youden's index was comparable with previous studies published.