Diagnostic utility of adenosine deaminase in exudative pleural effusions

OBJECTIVE To determine the diagnostic utility of adenosine deaminase (ADA) in exudative pleural effusions of different etiologies. SETTING AND DESIGN It was an observational study conducted at a tertiary care teaching institute. MATERIALS AND METHODS Of a total of 171 pleural fluid samples, 122 were found to be exudates and were included in the study. Pleural fluid ADA was done for all included patients. Pleural fluid ADA ≥40 U/l was taken as diagnostic cut off for TB effusion. STATISTICAL ANALYSIS Sensitivity, specificity positive and negative predictive value of pleural fluid ADA for diagnosing TB was calculated by using clinical calculator - 1, Richard Lowry 2001-2013. RESULTS There were 171 patients with pleural effusion, out of which 122 (71.8%) were found to be exudative and were studied further. There were 49 (40.1%), 36 (29.5%) and 33 (27%) cases of TB, malignancy and para pneumonic effusion respectively, whereas 4 (3.3%) cases remained undiagnosed. Median ADA values for TB, malignancy and para pneumonic effusion were 55.8 U/l (range 9.7-756 U/l), 18 U/l (6.5-81 U/l) and 25 U/l (3.4-172 U/l) respectively. Pleural fluid ADA >40U/l yielded 85.7% sensitivity, 80.8% specificity, 75% positive predictive value and 89.5% negative predictive value. CONCLUSION Pleural fluid ADA remains useful in diagnosing tuberculosis pleural effusion. The median ADA for TB effusion in present cohort was 51.8 IU/ml. Pleural fluid ADA of 40 U/L yielded 89.5% negative predictive value and 75% positive predictive value. Pleural fluid ADA is cost effective and good screening test for diagnosis of TB.