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Role of Nucleic Acid Amplification Tests (NAATs) in Tuberculous Pleural Effusion: Where It Fits In Routine Diagnostic Workup?

Patil Shital, Halkanche Gajanan and Ayachit Rujuta

Background: Commonest cause of pleural effusion in India is tuberculosis (TB) and poses a diagnostic difficulty because of the low sensitivity of culture technique.

Methods: Prospective study conducted during Jan 2012 to Sept. 2013 with an objective to find role of Nucleic acid amplification tests (NAATs) in tuberculous pleural effusion. We also observed comparison of NAATs i.e. MTB DNA PCR with other conventional diagnostic techniques like pleural fluid biochemistry, ADA (adenosine deaminase level), cytology and culture for mycobacterium tuberculosis, included 100 cases with signs, symptoms, history and radiological features suggestive of tuberculous pleural effusion. All the cases were subjected to pleural fluid analysis, smear for AFB, ADA, cytology, AFB culture on LJ media & MTB DNA PCR. Statistical analysis was done by using t-test and chi-test.

Results: Out of total 100 cases with pleural effusion, 09% cases were sputum positive for AFB, 3% pleural fluid samples positive for AFB, 28% were culture positive, 74% were DNA PCR positive, and 85% cases had ADA >40 units/liter, 87% cases had a LN Ratio greater than 0.75. Sensitivity, specificity, PPV & NPV of PCR for MTB was observed 92.86%, 33.33%, 35.13% & 92.30% respectively (p<0.01). In PCR positive cases, there was no significant association between ADA levels in pleural fluid culture for MTB positive and negative (P>0.4). In PCR negative cases; there was statistically significant association between ADA levels in pleural fluid culture for MTB positive and negative results. (P<0.05) Combined yield of pleural fluid culture, ADA>40 units/liter, DNA PCR and LN ratio >0.75 gave a positive diagnostic yield in 98% of cases, 2% with diagnostic dilemma were diagnosed by pleural biopsy. ATT response was observed in 78% cases in 2 weeks, 98% cases in 4 weeks and 100% cases at the end of 6 weeks.

Conclusion: In cases with exudative pleural effusion with Lymphocyte in pleural fluid >50% and L/N ratio>0.75 with ADA <40 units, MTB DNA PCR (NAATs) will be very useful in confirming tuberculosis as a cause for pleural effusion. Results of NAATs in this situation are very useful, sensitive, less time consuming and comparable to pleural fluid culture. Hence we recommend MTB DNA PCR in these cases.