Study of diagnostic utility of Xpert MTB/Rif test on pleural fluid in the evaluation of patients presenting with Pleural Tuberculosis in Nepal.

Abstract

Existing tests for the diagnosis of pleural tuberculosis (TB) have major limitations in terms of accuracy, time to diagnosis and drug resistance testing. A test which can diagnose pleural TB and detect resistance, like Xpert MTB/Rif, would be optimal for rapid diagnosis and treatment. A prospective observational study was done in a tertiary care hospital in Eastern Nepal. Fifty-one patients with clinic-radiologic suspicion of pleural TB were included. The results of pleural fluid Xpert MTB/Rif were compared with two Composite Reference Standards. Composite Reference Standard-1 consisted of positive pleural fluid smear, positive culture, positive histology of pleural biopsy, and positive sputum results. Composite Reference Standard-2 included those with Composite Reference Standard-1 and those with high ADA values (>40 U/l) with response to anti-tubercular treatment at 8 weeks of follow-up. Thirty-six patients were diagnosed as Pleural TB. Nine fulfilled Composite Reference Standard-1. Pleural fluid Xpert MTB/Rif was positive in five cases with Composite Reference Standard-1 and nine cases with Composite Reference Standard-2. The sensitivity, specificity, positive predictive value and negative predictive value with reference to Composite Reference Standard-1 were 55.56%, 88.10%, 50%, and 90.24%, respectively. Using Composite Reference Standard-2 as reference, sensitivity, specificity, positive predictive value and negative predictive value were 25%, 93.33%, 90%, and 34.15%, respectively. Two cases were diagnosed Xpert Rif resistant on pleural fluid. Due to low sensitivity, the Xpert MTB/Rif test cannot be recommended as initial test of diagnosis in a high prevalence setting. At the same time its clinical utility lies in testing of patients suspected to have drug-resistant pleural tuberculosis.