Adenosine Deaminase CD4 Cells Figure 1. Correlation plot of ADA in pleural fluid and blood CD4 counts in TB pleuritis patients (N = 129). doi:10.1371/journal.pone.0002788.g001 Mann-Whitney U values p- values 0.691 0.060 0.216 0.325 0.925 ,0.05* 0.181 0.054 patients [25]. This may be due to higher immune activation in HIV positive patients with very low CD4 counts [26]. Further- more, we did not find any correlation between ADA values and pleural fluid lymphocyte numbers or percentage in agreement with the study by Lee et al [27], but in contrast to other studies [12,28]. One explanation could be that the isoenzyme ADA-2 which contributes significantly to total ADA in diagnosing TPE is found mainly in the monocytes [29] which are not significantly affected in HIV patients compared to CD4 T-lymphocytes. Table 4. Group comparison of laboratory markers among total TB pleuritis patients with ,50 (N = 41) and .50 (N = 88) CD4 counts. Laboratory test (N) In pleural fluid Adenosine deaminase U/L (129) Lymphocyte cells/microL (86) Lymphocyte % (68) Lactate dehydro-genase U/L (115) Total protein g/L (105) In blood CD4 count cells/microL (129) Absolute Lymphocyte count X109/L (75) Red blood cells X 1012/L (111) * = significant difference between the 2 groups. doi:10.1371/journal.pone.0002788.t004 1725.5 586.0 401.5 1315.0 1211 ,0.05* 552.0 1044.5 Interferon gamma is considered to be a better marker than ADA for the diagnosis of tuberculous pleuritis, since its estimation is not affected by immununosuppression [30,31]. However, in our study the ADA assay performed well even at very low CD4 count below 10 cells/microL and the cost of estimating ADA is 20 times less than that of interferon gamma estimation. Therefore ADA analysis is more cost effective than the estimation of interferon gamma for the diagnosis of tuberculous pleuritis in developing countries [18]. We have shown that ADA offers a high sensitivity and is rapid for the diagnosis of tuberculous pleuritis in HIV patients with low Table 5. Correlation (r) values for ADA and other blood and pleural fluid markers in tuberculous pleuritis patients (N = 197). Test In blood CD4 counts cells/microL Absolute blood lymphocytes x 10 9/L Red blood cells x 1012/L In pleural fluid Leucocytes LYM% Lactate dehydro-genase U/L Total protein g/L r 20.14 20.049 20.044 0.028 0.110 0.152 0.045 p-values 0.114 0.667 0.644 0.798 0.373 0.104 0.649 LYM% = pleural fluid lymphocyte percentage of total leucocytes. doi:10.1371/journal.pone.0002788.t005 PLoS ONE | www.plosone.org 4 July 2008 | Volume 3 | Issue 7 | e2788