The utility of Xpert MTB/RIF performed on bronchial washings obtained in patients with suspected pulmonary tuberculosis in a high prevalence setting

Background: Xpert MTB/RIF has been shown to have a superior sensitivity to microscopy for acid fast bacilli (AFB) in sputum and has been recommended as a standard first line investigation for pulmonary tuberculosis (PTB). Bronchoscopy is a valuable tool in diagnosing PTB in sputum negative patients. There is limited data on the utility of Xpert MTB/RIF performed on bronchial lavage specimens. Our aim was to evaluate the diagnostic efficiency of Xpert MTB/RIF performed on bronchial washings in sputum scarce/negative patients with suspected PTB. Methods: All patients with a clinical and radiological suspicion of PTB who underwent bronchoscopy between January 2013 and April 2014 were included. The diagnostic efficiencies of Xpert MTB/RIF and microscopy for AFB were compared to culture for Mycobacterium tuberculosis. Results: Thirty nine of 112 patients were diagnosed with culture-positive PTB. Xpert MTB/RIF was positive in 36/39 with a sensitivity of 92.3 % (95 % CI 78-98 %) for PTB, which was superior to that of smear microscopy (41 %; 95 % CI 26.0-57.8 %, p = 0.005). The specificities of Xpert MTB/RIF and smear microscopy were 87.7 % (95 % CI 77.4-93.9 %) and 98.6 % (95 % CI 91.6 %-99.9 %) respectively. Xpert MTB/RIF had a positive predictive value of 80 % (95 % CI; 65-89.9 %) and negative predictive value of 95.5 % (95 % CI 86.6-98.8 %). 3/9 patients with Xpert MTB/RIF positive culture negative results were treated for PTB based on clinical and radiological findings. Conclusion: Xpert MTB/RIF has a higher sensitivity than smear microscopy and similar specificity for the immediate confirmation of PTB in specimens obtained by bronchial washing, and should be utilised in patients with a high suspicion of pulmonary tuberculosis.