Evaluation of adenosine deaminase (ADA) and ADA1 and ADA2 isoenzyme activities in patients with pulmonary tuberculosis and tuberculous pleurisy

ObjectivesTuberculosis (TB) still remains an important medical problem due to high levels of morbidity and mortality worldwide. Tuberculous pleurisy is the most common form of extrapulmonary TB. Since tuberculous pleural effusion usually contains a low number of mycobacteria, the diagnostic sensitivity of both direct microscopy and pleural fluid cultures is relatively low.Adenosine deaminase (ADA) is an essential enzyme in the metabolism of purine nucleosides. For an adequate interpretation of ADA, it is important to highlight the fact that ADA is represented by two isoenzymes: ADA1 and ADA2. The ADA1 isoenzymes are found in all cells, with the highest activity in lymphocytes, whereas ADA2 isoenzymes appear to be found only in antigen-presenting cells.The aim of this study is to evaluate the ADA and ADA1 and ADA2 isoenzyme activity in patients with pulmonary TB and tuberculous pleurisy.MethodsThis study included 25 patients with pleural effusions (11 with pleural TB and 14 with nontuberculous etiologies), 35 patients with pulmonary tuberculosis (PTB) and 42 healthy subjects.Total ADA activity level in pleural fluid and blood plasma was measured by the “ADA-test kit” developed in the Republican Scientific and Practical Center for Epidemiology & Microbiology (Minsk, Belarus). The principle “ADA-test” is a colorimetric method in which adenosine is deaminated by ADA and the free ammonia is estimated. Estimated ADA2 activity was calculated from the ADA and 2′-deoxyadenosine deaminase activities using the affinity of ADA2 for the two substrates.ResultsThe mean plasma ADA level in patients with PTB was 19.2±3.3U/L that was significantly higher than the control group (10.4±0.6U/L). The difference between patients with pleural TB and the controls is also significant (18.2±2.5U/L versus 10.4±0.6U/L, p<0.05). A significantly higher activity of ADA1 and ADA2 in the blood plasma was observed in patients with PTB and pleural TB than those of the corresponding controls (p<0.05).With diagnostic thresholds of 12.5 and 16U/L respectively, the sensitivities of plasma ADA for PTB and pleural TB were 54% and 64%; their specificities 68% and 78%; AUC – 0.67 and 0.73, respectively.The ADA level in the pleural fluid was significantly higher in patients with TB pleural effusion. It was found that the mean ADA level in the pleural fluid was 74.6±7.9U/L in cases of pleural TB, as compared with 21.9±4.3U/L in non-tuberculosis effusion (p<0.05). These results indicate that pleural fluid ADA1 and ADA2 levels were higher in patients with pleural TB as compared with non-tuberculosis effusion.An analysis of the ROC curve for pleural fluid ADA activity showed that at the most accurate cut-off level of 53.4U/L, the sensitivity of the test for tuberculous pleurisy was 91% and the specificity was 93%.ConclusionThis study concluded that pleural fluid ADA analysis could be an easy, cheap and highly sensitive and specific test for the diagnosis of pleural TB