• Am. J. Respir. Crit. Care Med. · Mar 2019

    Comparative Study

    Xpert MTB/RIF Assay as a Substitute for Smear Microscopy in an Intermediate Burden Setting.

    • Hyun-Seung Lee, Seung-Jung Kee, Ju-Hyeon Shin, Yong-Soo Kwon, Sejong Chun, Jun Hyung Lee, Eun Jeong Won, Hyun-Jung Choi, Soo Hyun Kim, Myung-Geun Shin, Jong-Hee Shin, and Soon-Pal Suh.
    • 1 Department of Laboratory Medicine, Chonbuk National University Hospital, Jeonju, Republic of Korea.
    • Am. J. Respir. Crit. Care Med. 2019 Mar 15; 199 (6): 784-794.

    RationaleUse of Xpert MTB/RIF assay as a substitute for smear microscopy in routine clinical practice remains unexplored in an intermediate-tuberculosis-burden setting.ObjectivesTo compare the diagnostic performance of Xpert and smear microscopy, based on sampling time and location, correlation of Xpert semiquantitative category with smear grade and time to culture positivity, and compliance of reporting time with defined standard time.MethodsConsecutive sputum samples collected from 2,952 suspected pulmonary tuberculosis patients over a 3-year period were tested by Xpert, smear microscopy, and liquid culture as part of routine diagnostics in South Korea.Measurements And Main ResultsBased on the analysis of a single sputum specimen per patient, of 2,952 samples, 263 (8.9%) were culture-confirmed tuberculosis and 265 (9.0%) were nontuberculous mycobacteria. The overall sensitivity and specificity were 74.1% and 97.5% for Xpert versus 38.8% and 96.7% for smear microscopy, respectively (P < 0.0001; P > 0.05). Of 82 smear-positive nontuberculous mycobacteria, 81 (98.8%) were accurately excluded by Xpert. Sampling time and location significantly affected the performance of smear microscopy but not that of Xpert. Xpert semiquantitative category strongly correlated with smear grade (γGoodman-Kruskal = 0.982; P < 0.0001) and time to culture positivity (γGoodman-Kruskal = -0.962; P < 0.0001). Median reporting time and its compliance rate within 24 hours were 3.1 hours and 96.3% for Xpert versus 19.1 hours and 88.7% for smear microscopy, respectively (P < 0.0001; P < 0.05).ConclusionsXpert provides faster, more stable, and superior results compared with smear microscopy, in addition to its strong correlation with smear grade. Xpert might replace smear microscopy as the first-line diagnostic test for pulmonary tuberculosis in routine clinical practice in an intermediate-burden setting.

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