1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos 1 2 4 7 13 12 15 18 19 19 19 20 30 32 33 33 35 38 40 40 40 41 43 45 46 46 55 41 86 4 98 200 21 42 210 55 71 52 56 51 55 132 124 48 112 93 70 200 71 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 HIV pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos pos neg neg 55 55 57 60 64 65 66 66 70 74 75 77 79 80 80 105 115 121 132 163 168 179 180 200 200 208 229 241 251 302 401 482 512 38 60 60 112 112 61 133 51 36 112 186 73 43 53 38 1 88 44 53 64 35 44 38 49 67 96 107 113 102 100 35 70 28 Table 3. HIV status, CD4 counts and ADA values for the 2 groups with ,50 (N = 25) and .50 (N = 33) CD4 counts among confirmed TB pleuritis patients. CD4,50 cells/microL CD4 .50 cells/microL Case HIV CD4 ADA CD4 ADA Adenosine Deaminase CD4 Cells TB pleuritis respectively. The four patients with CD4 cell counts of less than 10 cells/microL (1, 2, 4, and 7 cells/microL) among confirmed TB pleuritis patients had ADA values above the cut-off with values of 46, 55, 41, and 86 U/L, respectively (Table 3). There was no correlation between ADA values and blood CD4 cell counts (Figure 1). There was no statistical difference in the absolute blood lymphocyte count; pleural fluid lymphocytes number or percent- age, lactate dehydrogenase and total protein between patients with CD4 cell counts ,50 and .50 cells/microL when group comparison was made with non parametric Mann-Whitney U test (Table 4). Furthermore there was no correlation between ADA values and blood CD4 counts, absolute lymphocyte count and red cell counts in blood or lymphocyte counts and percentage, lactate dehydro- genase and total protein in pleural fluid (Table 5). Discussion We have evaluated the usefulness of the ADA assay in predominantly HIV positive patients with very low CD4 counts. The overall sensitivity of the ADA assay in diagnosing tuberculous pleuritis was 94%. This finding is similar to that reported in a number of studies [12,14,18,19,20]. However this is the first study demonstrating high sensitivity of the ADA assay in HIV patients with very low CD4 cell counts. As shown in our study there was no significant difference in sensitivity when comparing cases with CD4 cell counts of less than 50 cells/microL to those with CD4 counts greater than 50 cells/microL. In fact, the mean ADA value was higher in the group with the lower CD4 cell count. The ADA is useful for the diagnosis of TB pleuritis since the result is available on the same day compared to culture which takes about 2 weeks. This allows for rapid institution of TB treatment leading to improvement in patient outcome[21]. Furthermore the positive likelihood ratio (LR) was .10 and the negative likelihood ratio was ,0.1, this implies that the ADA is useful in clinical practice to rule in and rule out TB pleuritis. The advantage of LR is that it is not affected by prevalence of disease as opposed to positive predictive value. Previous studies evaluating the usefulness of ADA for the diagnosis of tuberculous pleuritis have either a very small number of HIV positive cases [22] or patients with higher mean CD4 counts [14]. Hsu et al [13] have shown a low sensitivity for ADA in tuberculous pleural effusion in immunocompromised chronic diseases patients, however only 10 patients were evaluated and the HIV status was not determined. Corral et al [23] reported a similar low sensitivity in HIV positive tuberculous meningitis cases whilst Reuter et al [15] reported low sensitivity of ADA in tuberculous pericarditis patients with advanced HIV disease compared to cases with higher CD4 cell count. The difference in the outcome of our retrospective study compared with that of Reuter et al may be due to the fact that majority of the patients in this study had lower CD4 cell counts. Different cut-off values ranging from10 to 71 U/L have been used for positive ADA test, but the type of ADA assays has not shown any variations in sensitivity [24]. The cut-off value of 30 U/ L for tuberculous pleuritis as used in this study is expected to offer a specificity of 98% [17] and is used in the clinical setting at our institution and by most laboratories in South Africa. We did not find any correlation between the ADA values and CD4 cell counts. Even at CD4 counts of less than 10cells/microL, the ADA values were still above the cut-off. We also did not find any correlation between ADA values and CD4 cell counts in another cohort of South African HIV infected TB pleuritis pos = positive, neg = negative, = not available, ADA = adenosine deaminase. doi:10.1371/journal.pone.0002788.t003 .50 cells/microL, (p,0.05) and the corresponding values among total TB cases was 29 and153 (p,0.05) respectively. The sensitivity and specificity of ADA was 94% and 95% respectively as shown in table 2. The positive and negative likelihood ratio was 19 and 0.06 respectively. The mean ADA values for the different categories is shown in table 3. The mean ADA value was highest in tuberculous pleuritis except for Kaposi sarcoma, and empyema in which the ADA gave false positive result. The sensitivity of ADA was not affected by low CD4 cell count. In addition, there was no significant difference in the mean ADA value in patients with lower CD4 counts (81 U/L655.1); (76 U/L645.3) compared to those with higher CD4 cell counts (70 U/L637.8); (72 U/L640.6), (p.0.5) among confirmed and total PLoS ONE | www.plosone.org 3 July 2008 | Volume 3 | Issue 7 | e2788