tuberculosis remains a frequent and important infectious disease worldwide , it occurs with , in approximately 30% of all cases , extrapulmonary involvement in the form of tuberculous pleurisy ( tp ) . and tp increases the morbidity and mortality associated with tuberculosis , and it is a major economic and health burden all over the world . the differential diagnosis of tp reliably is challenging although many conventional diagnostic methods are used , including microscopic analysis of pleural fluid or sputum smears , culturing for mycobacteria and even performing a pleural biopsy . each of these methods has significant limitations : microscopic analysis of pleural fluid is rarely positive ( < 5% ) , culture of pleural fluid shows poor sensitivity ( 24 - 58% ) , culturing for mycobacterium tuberculosis requires several weeks , and pleural biopsy , which is considered the best method for confirming tp diagnosis , is invasive and technically difficult . even more invasive procedures such as thoracoscopy or thoracotomy have been used for differential diagnosis of tp , but these complex procedures can cause complications and even increase morbidity . these led investigators to explore several biomarkers as possible diagnostic indicators . its release by mesothelial cells in pleura contributes to the occurrence and development of tp through three mechanisms : it acts as a proinflammatory cytokine to attract neutrophils to kill mycobacteria directly as part of an innate immune response ; it acts synergistically with interferon ( ifn- ) to activate macrophages as part of an adaptive immune response ; and it recruits nave t cells to the granuloma . tumor necrosis factor- ( tnf- ) levels in the pleural fluid are significantly higher in patients with tuberculosis than in patients with pulmonary malignancy . some studies have reported that levels of tnf- in pleural fluid provide high diagnostic sensitivity ( 96.0% ) and specificity ( 93.0% ) . other studies , however , have reported much lower corresponding values of 70% and 66% . however , the comprehensive picture of the diagnostic usefulness of tnf- levels in pleural fluid is not obvious . therefore in this article we will product a meta - analysis to explore the diagnostic accuracy of pleural fluid tnf- in tp . we conducted this meta - analysis according to the guidelines of the prisma and the quality assessment of diagnostic accuracy studies ( quadas ) checklist . the following search terms were used :  tuberculosis  or  tb disease  or  active tuberculosis  or tnf - alpha  or  cytokines  and  sensitivity  and  specificity  and  diagnosis  . reference lists of articles identified in these searches were also searched manually . to be included in our study , studies had to 
 evaluate the sensitivity and/or specificity of pleural fluid tnf- for diagnosis of tp using.a case - control design involving.case and control groups classified using clear diagnostic criteria and.the same method to assay tnf-.apply an adequate experimental method . evaluate the sensitivity and/or specificity of pleural fluid tnf- for diagnosis of tp using . a case - control design involving . case and control groups classified using clear diagnostic criteria and . the same method to assay tnf-. apply an adequate experimental method . unpublished data , abstracts , review articles , and letters to the editor were excluded . two reviewers ( z.l . and w.q . ) independently assembled a final set of eligible studies , and a third author ( x.c . ) the same procedure was followed to extract data from the included studies using a standardized form . extracted data included first author , publication year , country of the study , number and characteristics of participants , tnf- assay method , cut - off value for tnf- detection , sensitivity and specificity , and numbers of true positives , false positives , true negatives and false negatives . we assessed the methodological quality of the studies using the quadas-2 checklist , with a maximum score of 11 . analyses were performed using stata and meta - disc ( xi cochrane colloquium , barcelona , spain ) . the following measures of test accuracy were computed for each study : sensitivity , specificity , positive likelihood ratio ( plr ) , negative likelihood ratio ( nlr ) and diagnostic odds ratio ( dor ) . these curves were plotted for each study using the sensitivity and specificity based on the single - test threshold identified within the same study . then we performed a meta - regression analysis to assess the effect of the baseline in each study on the relative dor of pleural fluid tnf- in tp diagnosis . we used a random - effect model to meta - analyze sensitivity , specificity , and other diagnostic measures across multiple studies . to assess statistically significant variability ( heterogeneity ) across studies , we used chi - squared and fisher 's exact tests . the following search terms were used :  tuberculosis  or  tb disease  or  active tuberculosis  or tnf - alpha  or  cytokines  and  sensitivity  and  specificity  and  diagnosis  . only english - language articles were considered . reference lists of articles identified in these searches were also searched manually . to be included in our study , studies had to 
 evaluate the sensitivity and/or specificity of pleural fluid tnf- for diagnosis of tp using.a case - control design involving.case and control groups classified using clear diagnostic criteria and.the same method to assay tnf-.apply an adequate experimental method . evaluate the sensitivity and/or specificity of pleural fluid tnf- for diagnosis of tp using . a case - control design involving . case and control groups classified using clear diagnostic criteria and . the same method to assay tnf-. apply an adequate experimental method . unpublished data , abstracts , review articles , and letters to the editor were excluded . two reviewers ( z.l . and w.q . ) independently assembled a final set of eligible studies , and a third author ( x.c . ) the same procedure was followed to extract data from the included studies using a standardized form . extracted data included first author , publication year , country of the study , number and characteristics of participants , tnf- assay method , cut - off value for tnf- detection , sensitivity and specificity , and numbers of true positives , false positives , true negatives and false negatives . we assessed the methodological quality of the studies using the quadas-2 checklist , with a maximum score of 11 . analyses were performed using stata and meta - disc ( xi cochrane colloquium , barcelona , spain ) . the following measures of test accuracy were computed for each study : sensitivity , specificity , positive likelihood ratio ( plr ) , negative likelihood ratio ( nlr ) and diagnostic odds ratio ( dor ) . these curves were plotted for each study using the sensitivity and specificity based on the single - test threshold identified within the same study . then we performed a meta - regression analysis to assess the effect of the baseline in each study on the relative dor of pleural fluid tnf- in tp diagnosis . we used a random - effect model to meta - analyze sensitivity , specificity , and other diagnostic measures across multiple studies . to assess statistically significant variability ( heterogeneity ) across studies , we used chi - squared and fisher 's exact tests . literature searches turned up 96 potentially eligible studies , and 86 were excluded based on review of titles and abstracts . the remaining 10 articles were read in full , and 4 were excluded because they did not apply an adequate experimental method . in the end , six publications assessing the diagnostic performance of pleural fluid tnf- assay in tp were included in our analysis . one study involved two control groups , and sufficient data were reported for both that we were able to treat the groups as two independent studies in the meta - analysis [ figure 1 ] . flow diagram of included and excluded studies characteristics of studies included in the meta - analysis the seven studies involved 159 patients with tp and 338 without it . average sample size in the seven studies was 71 ( range : 50 - 97 ) . tnf- levels in all studies were assayed by enzyme - linked immunosorbent assay ( elisa ) . sensitivity for pleural fluid tnf- in tp diagnosis ranged from 0.71 to 0.96 in the seven studies , and meta - analysis of sensitivity and specificity indicated a pooled sensitivity of 0.89 ( 95% confidence interval [ ci ] : 0.83 - 0.93 ) [ figure 2 ] . specificity ranged from 0.71 to 0.93 , and meta - analysis showed a pooled specificity of 0.82 ( 95% ci : 0.78 - 0.86 ) [ figure 2 ] . plr was 4.78 ( 95% ci : 3.32 - 6.89 ) and nlr was 0.16 ( 95% ci : 0.1 - 0.27 ) [ figure 3 ] . dor was 32.43 ( 95% ci : 14.48 - 72.6 ) [ figure 4 ] . significant heterogeneity ( i > 50% ) was present among the seven studies with respect to plr data but not data for other diagnostic measures : i was 0% for sensitivity , 47.5% for specificity , 53.8% for plr , 25% for nlr , and 46.9% for dor . forest plot of estimates of sensitivity / specificity for pleural fluid tnf- in the diagnosis of tuberculous pleurisy . point estimates of sensitivity and specificity from each study are shown as solid circles , the size of which reflects the total number of cases and controls . numbers indicate the reference numbers of the studies forest plot of estimates of positive and negative likelihood ratios ( plr and nlr ) for pleural fluid tnf- in the diagnosis of tuberculous pleurisy . point estimates of plr and nlr from each study are shown as solid circles , the size of which reflects the total number of cases and controls . numbers indicate the reference numbers of studies ( a ) forest plot of estimates of diagnostic odds ratios for pleural fluid tumor necrosis factor- ( tnf- ) in the diagnosis of tuberculous pleurisy . point estimates of diagnostic odds ratios from each study are shown as solid circles , the size of which reflects the total number of cases and controls . ( b ) summary receiver operating characteristic curves for pleural fluid tnf-. each study is depicted as a solid circle , the size of which reflects the total number of cases and controls summary receiver operating characteristic curves were generated by plotting sensitivity against ( 1-specificity ) for individual studies [ figure 4 ] . the curves did not lie near the desired upper left corner , and the maximum joint sensitivity and specificity was 0.89 , with an area under the curve ( auc ) of 0.8556 ( standard error of mean 0.0559 ) . on the other hand , dor was 32.43 , suggesting relatively high overall accuracy . across the seven studies , tnf- cut - off values in the elisa and different diseases in the control group were different significantly [ table 1 ] . weighted meta - regression of the effects of diseases in control groups and cut - off values on diagnostic accuracy of pleural fluid tnf- funnel plots showed some asymmetry [ figure 5 ] , presumably reflecting the small number of studies included in our meta - analysis . nevertheless , deeks test gave a p = 0.11 , suggesting that our analysis did not carry significant risk of publication bias . funnel plot for evaluating publication bias among the six articles ( seven studies ) included in the meta - analysis . the log of the diagnostic odds ratio ( dor ) is plotted against the standard error of log dor ; the latter serves as an indicator of sample size . average sample size in the seven studies was 71 ( range : 50 - 97 ) . tnf- levels in all studies were assayed by enzyme - linked immunosorbent assay ( elisa ) . sensitivity for pleural fluid tnf- in tp diagnosis ranged from 0.71 to 0.96 in the seven studies , and meta - analysis of sensitivity and specificity indicated a pooled sensitivity of 0.89 ( 95% confidence interval [ ci ] : 0.83 - 0.93 ) [ figure 2 ] . specificity ranged from 0.71 to 0.93 , and meta - analysis showed a pooled specificity of 0.82 ( 95% ci : 0.78 - 0.86 ) [ figure 2 ] . plr was 4.78 ( 95% ci : 3.32 - 6.89 ) and nlr was 0.16 ( 95% ci : 0.1 - 0.27 ) [ figure 3 ] . dor was 32.43 ( 95% ci : 14.48 - 72.6 ) [ figure 4 ] . significant heterogeneity ( i > 50% ) was present among the seven studies with respect to plr data but not data for other diagnostic measures : i was 0% for sensitivity , 47.5% for specificity , 53.8% for plr , 25% for nlr , and 46.9% for dor . forest plot of estimates of sensitivity / specificity for pleural fluid tnf- in the diagnosis of tuberculous pleurisy . point estimates of sensitivity and specificity from each study are shown as solid circles , the size of which reflects the total number of cases and controls . numbers indicate the reference numbers of the studies forest plot of estimates of positive and negative likelihood ratios ( plr and nlr ) for pleural fluid tnf- in the diagnosis of tuberculous pleurisy . point estimates of plr and nlr from each study are shown as solid circles , the size of which reflects the total number of cases and controls . numbers indicate the reference numbers of studies ( a ) forest plot of estimates of diagnostic odds ratios for pleural fluid tumor necrosis factor- ( tnf- ) in the diagnosis of tuberculous pleurisy . point estimates of diagnostic odds ratios from each study are shown as solid circles , the size of which reflects the total number of cases and controls . ( b ) summary receiver operating characteristic curves for pleural fluid tnf-. each study is depicted as a solid circle , the size of which reflects the total number of cases and controls summary receiver operating characteristic curves were generated by plotting sensitivity against ( 1-specificity ) for individual studies [ figure 4 ] . the curves did not lie near the desired upper left corner , and the maximum joint sensitivity and specificity was 0.89 , with an area under the curve ( auc ) of 0.8556 ( standard error of mean 0.0559 ) . on the other hand across the seven studies , tnf- cut - off values in the elisa and different diseases in the control group were different significantly [ table 1 ] . weighted meta - regression of the effects of diseases in control groups and cut - off values on diagnostic accuracy of pleural fluid tnf- funnel plots showed some asymmetry [ figure 5 ] , presumably reflecting the small number of studies included in our meta - analysis . nevertheless , deeks test gave a p = 0.11 , suggesting that our analysis did not carry significant risk of publication bias . funnel plot for evaluating publication bias among the six articles ( seven studies ) included in the meta - analysis . the log of the diagnostic odds ratio ( dor ) is plotted against the standard error of log dor ; the latter serves as an indicator of sample size . given the numerous limitations associated with current methods for diagnosing tp , researchers have explored whether pleural fluid biomarkers such as tnf- can serve as diagnostic markers . these studies have given conflicting results about the diagnostic performance of pleural fluid tnf- , so here we meta - analyzed the available evidence . our analysis suggests that pleural fluid tnf- measurements by themselves are not sufficiently sensitivity ( 0.89 ) and specificity ( 0.82 ) to diagnose tp , but they can provide complementary diagnostic information when used in combination with assays of other pleural fluid biomarkers and conventional tests such as bacteriological examination or pleural biopsy . a meta - analysis of the seven included studies indicated a pooled dor of 32.4 for the pleural fluid tnf- assay , indicating a relatively high accuracy . dor , which combines sensitivity and specificity data that serves as an aggregate indicator of test accuracy , is the ratio of the odds of positive test results in individuals with disease relative to the odds of positive test results in individuals without disease . the sroc curve and its auc present an overall summary of test performance and display the trade - off between sensitivity and specificity . in the present meta - analysis , we found the sensitivity of the pleural fluid tnf- assay to be 0.89 ; specificity , 0.82 ; maximum joint sensitivity and specificity , 0.89 ; and auc , 0.8556 . diagnostic odds ratio and sroc curve analysis are not easy to interpret and use in clinical practice , and likelihood ratios are considered more clinically meaningful . therefore , we meta - analyzed the data to determine pooled plr and nlr as measures of diagnostic accuracy . the plr value of 4.78 suggested that the probability of being positive for pleural fluid tnf- was nearly 5-fold higher for patients with tp than for patients without it . although this is insufficient to serve as the sole basis for diagnosing tp , it is likely to be sufficient to allow a clinician to decide whether to initiate or continue anti - tuberculosis treatment of tp in individuals who do not present evidence of malignancy or inflammation . at the same time , nlr was 0.16 in our meta - analysis , indicating that patients negative for pleural fluid tnf- still have a 16% chance of having tp . this provides further evidence that such an assay is inadequate , on its own , for ruling out tp . thus , a negative pleural fluid tnf- assay is not sufficient cause to deny or discontinue anti - tuberculosis therapy . the reliability of meta - analyses depends on heterogeneity among the included studies , and we found significant heterogeneity in the data for plr . since the causes of heterogeneity can reveal systematic factors affecting the accuracy and reliability of meta - analyses , we examined the seven studies more carefully . in all studies , tp was diagnosed based on bacteriology , histology or both ; tnf- was determined using an elisa kit according to the manufacturer 's guidelines ( oxfordimmunotec ltd . , abingdon , uk ) ; and the quadus-2 score in each study was relatively high . in addition , inter - study variation in tnf- cut - off values and baseline tnf- levels in the control groups did not substantially affect diagnostic accuracy . therefore , the basis for the heterogeneity in plr data in our meta - analysis is unclear , and in any case , further large studies are needed to verify our findings , especially since we excluded possibly relevant studies that were not published in english or that were published only as conference abstracts or letters to the editor . analyses of other pleural fluid biomarkers suggest that they , like tnf- , can not be used alone as diagnostic indicators . a meta - analysis of the diagnostic accuracy of ifn - g in tp reported a sensitivity of 0.75 , specificity of 0.82 , plr of 3.49 , nlr of 0.24 , and dor of 19.04 . diagnostic performance was better in meta - analysis of adenosine deaminase , which reported a sensitivity of 0.86 , specificity of 0.88 , plr of 6.32 , nlr of 0.15 , and dor of 45.25 . these results suggest none of the biomarkers is sufficient on its own . assaying for multiple biomarkers may improve the accuracy of tp diagnosis , and such combined approaches should include tnf- because the peptide plays such an important role in tuberculosis pathogenesis , especially in patients with auto - immune diseases who are taking tnf- antagonists . the available evidence suggests that the pleural fluid tnf- assay should not be used on its own to diagnose tp or guide treatment decisions , but it can be used to complement other tests including microscopic smear examination , culture for m. tuberculosis , pleural tissue histology and response to anti - tuberculosis therapy . the diagnostic performance of tnf- may improve by changing the detection platform from the current elisa to more advanced flow cytometry , elispot and luminex methods . lz searched the literature and assessed articles , extracted data , performed meta - analyses , and wrote the draft . cx contributed in the conception of the work , revised the draft , approval of the final version of the manuscript , and agreed for all aspects of the work .
background : pleurisy is a common extra pulmonary complication of tuberculosis , but current methods for diagnosing it are fairly crude . here we product a meta - analysis for the available evidence on the ability of tumor necrosis factor- ( tnf- ) in pleural fluid to serve as a diagnostic marker of tuberculous pleurisy ( tp).materials and methods : we searched the pubmed , embase , and google scholar databases systematically for studies measuring sensitivity , specificity and other measures of diagnostic accuracy of pleural fluid tnf- in the diagnosis of tp were meta - analyzed by stata , version 12 and meta-disc.results:a total of six publications reporting seven case - control studies were identified . 
 pooled results indicated that pleural fluid tnf- showed a diagnostic sensitivity of 0.89 ( 95% confidence interval [ 95% ci ] 0.83 - 0.93 ; range , 0.42 - 1.0 ) and a diagnostic specificity of 0.82 ( 95% ci : 0.78 - 0.86 ; range , 0.58 - 0.98 ) . 
 the pooled positive likelihood ratio was 4.78 ( 95% ci : 3.32 - 6.89 ) ; the negative likelihood ratio , 0.16 ( 95% ci : 0.1 - 0.27 ) ; the diagnostic odds ratio , 32.43 ( 95% ci : 14.48 - 72.6 ) ; and the area under the curve was 0.8556 ( standard error of mean 0.0559).conclusion : pleural fluid tnf- levels shows relatively high sensitivity but insufficient specificity for diagnosing tp . 
 pleural fluid tnf- measurement may be useful in combination with clinical manifestations and conventional tests such as microbiological examination or pleural biopsy .