Evaluation of Xpert® MTB/RIF for the Detection of Mycobacterium Tuberculosis in Sputum-Smear Negative Patients Using Bronchoalveolar Lavage Fluid

Abstract BackgroundAn estimated three million cases of tuberculosis (TB) are missed annually and much time elapse for the diagnosis of suspected sputum-smear negative cases, hence, the need for rapid and accurate diagnostic test. This retrospective study was conducted to evaluate the use of the Xpert®MTB/RIF assay on BALF specimens in TB diagnosis in terms of time to treatment initiation and its effect on empirical treatment.MethodsBronchoscopy was offered to sputum smear-negative patients with suspected pulmonary tuberculosis (PTB). Collected BALF was tested by fluorescent microscopy, MGIT960, and Xpert®MTB/RIF assay. First-line drug sensitivity tests were performed on positive samples. Similar tests were done using sputum.ResultsBetween November 2017 and November 2019, a total of 395 suspected TB patients underwent bronchoscopy in our hospital. BALF samples were collected and analysed using different methods. Using BALF culture as the standard reference test, the sensitivity and specificity of Xpert®MTB/RIF for TB diagnosis using BALF specimens were 79.2% and 95.8%, respectively. The positive and negative predictive values were 87.5% and 93.0%, respectively. Rifampin resistance was highly predictive of multidrug resistant tuberculosis (MDR-TB) using Xpert®MTB/RIF, with a value of 72.7%.The median time to treatment initiation using BALF was 5 days (IQR=4-7 days) for fluorescent staining, 6 days (IQR=3-8 days) with Xpert®MTB/RIF and 31 days (IQR=29-35 days) for culture.Further, 179(45.3%) out of the 395 sputum smear-negative patients suspected of PTB were already started on empirical treatment before bronchoscopy. After bronchoscopy, 96(24.3%) tested positive for TB whilst 83(21%) tested negative with Xpert®MTB/RIF using BALF.ConclusionXpert®MTB/RIF done using BALF for sputum smear-negative patients suspected of PTB increases the diagnostic accuracy of TB and decreases the time to treatment initiation of PTB as well as the rate of empirical treatment use.