Table 1. The mean ADA values in the different diagnostic category. Cases Malignancy* (N = 26) Congestive heart failure (N = 12) Streptococcus pneumoniae effusion (N = 1) Klebsiella pneumoniae empyema (N = 1) Total TB pleuritis (N = 197) Mean ADA (U/L) 6SD 12.9613.1 7.1666.2 11 200 71.2639.6 SD = standard deviation; *Kaposi sarcoma is the only malignancy with ADA of 73 above the cut-off. doi:10.1371/journal.pone.0002788.t001 50 are regarded as very low and are an indication for disease progression [16]. However, it is not known how the ADA will perform for the diagnosis of tuberculous pleuritis, a common extra-pulmonary location in severely immunocompromised HIV patients. The aim of this study was to evaluate the sensitivity of ADA in tuberculous pleuritis patients with low CD4 counts and to determine whether there was any correlation between CD4 cell counts and ADA values. Materials and Methods Patients were identified through tracing of pleural fluid specimens sent for culture to the microbiology laboratory at the Dr George Mukhari (DGM) Hospital Ga-Rankuwa, Pretoria, South Africa. All patients presenting with pleural effusion had pleural tap and subsequently pleural fluid examination. Patients were put on TB treatment after pleural tap if there was strong suspicion of TB based on clinical features such as, history of contact with TB patients, TB history, chronic cough, night sweats, fever and loss of weight. The diagnosis of TB pleuritis was confirmed if culture of Mycobacterium tuberculosis in pleural fluid or tissue was positive or there was caseous granuloma in the pleural biopsy and was probable if; (1) there were clinical features such as history of TB contact, past history of TB, chronic cough, night sweats, fever and loss of weight; and (2) had clinical diagnosis of TB and started on TB treatment in the absence of any other cause of effusion. The control non- TB pleuritis group include; (1) malignant pleural effusion confirmed by cytological examination of pleural fluid/ histological examination of pleural biopsy; (2) Pleural effusion of other known etiology such as congestive cardiac failure or para- pneumonic effusion. Cases without ADA results were excluded from the analysis. The clinical records of patients as described above for the period January 2004 to January 2007 were reviewed. Data regarding clinical presentation (cough, fever, chest pain, night sweats, loss of Table 2. Validity of ADA as a diagnostic test. Cases Confirmed TB pleuritis (n = 72) Clinical TB (n = 125) Total TB Pleuritis (n = 197) 94 (86–98) 94 (88–97) 94 (90–97) Adenosine Deaminase CD4 Cells weight, diarrhoea, oral thrush), acid fast staining (AFB) and culture results of pleural fluid, HIV status, blood CD4 cell counts, and biochemical parameters in pleural fluid (ADA, lactate dehydroge- nase , total protein) were collected. The ADA was analysed using a commercial colorimetric assay kit (Diazyme General Atomics, CA). The cut-off value for positive ADA result was 30 U/L according to clinical practice at this hospital [17]. The patients were stratified according to the CD4 count as follows, ,50 and .50, cells/microL as referred above [16]. The study was evaluated and approved by the Research, Ethics and Publications Committee at the DGM Hospital, University of Limpopo, South Africa and the Regional Committee for Ethics in Medical Research in Bergen, Norway. Statistical analysis Data analysis was made by SPSS (SigmaStat; SPSS Inc; Chicago, IL). Mean, correlation coefficient, and group comparison was made with non parametric Mann-Whitney U test. Results A total of 300 pleural fluid samples were submitted to the laboratory for the diagnosis of TB over the 3 year study period of which 237 with available ADA results were included in the study. There were 197 TB pleuritis patients: mean age 35 years with 107 females and 40 non-TB pleuritis patients: mean age 50 years with 19 females. Among the TB pleuritis patients, 72 were confirmed TB pleuritis while the non-TB pleuritis included 26 malignancies (adenocarcinoma, mesothelioma, squamous cell carcinoma, met- astatic liver carcinoma, bronchial carcinoma and Kaposi sarco- ma), 10 congestive cardiac failures, 2 hydrothorax, 1 Streptococcus pneumoniae effusion and 1 Klebsiella pneumoniae empyema. The mean ADA for each category is shown in Table 1. The ADA value was positive, above the cut-off of 30 U/L in 186 of the 197 TB patients giving a sensitivity of 94% (Table 2). The mean ADA value was 71.2U/L whilst the mean total protein value was 51 g/dl. Among the 125 probable TB pleuritis patients; 89 were HIV positive, 18 were HIV negative and HIV was not available for 18 patients. The median ADA values were 64 U/L and 58 U/L for HIV positive and HIV negative respectively. CD4 cell counts were available for 58 of the 72 patients among the confirmed TB pleuritis patients. Fifty-one (88%) of the patients with known CD4 cell counts were confirmed HIV positive, whereas two were HIV negative with CD4 cell counts of 482 and 512 cells/microL. For five of the TB pleuritis patients the HIV was not documented, but as the patients had CD4 cell counts in the range of 19–208 cells/microL they were most likely HIV positive. The ADA values with corresponding CD4 cell counts ,50 and .50 cells/microL among confirmed TB pleuritis patients are presented in table 3. The mean CD4 cell counts in the confirmed TB pleuritis cases was 26 cells/microL in patients with CD4,50 cells/microL and 158 cells/microl in patients with CD4 count Sensitivity % (CI) Specificity % (CI) PPV % (CI) NPV (%) (CI) LR+ (CI) 95 (82–99) 95 (82–99) 95 (82–99) 97 (89–99) 98 (93–100) 99 (96–100 90 (76–97) 84 (70–93) 77.5 (63–88) 18.9 (4.9–73 18.9 (4.9–73.0) 18.9 (4.9–72.9) LR2 (CI) 0.06 (0.02–0.15) 0.06 (0.03–0.12) 0.06 (0.03–0.10) PPV = positive predictive value; NPV = negative predictive value; CI = 95% confidence interval; LR+ = positive likelihood ratio; LR2 = negative likelihood ratio. doi:10.1371/journal.pone.0002788.t002 PLoS ONE | www.plosone.org 2 July 2008 | Volume 3 | Issue 7 | e2788