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Updated: May 18, 2026
Diagnosing Pulmonary Tuberculosis with the Xpert MTB/RIF Test
Published on: April 9, 2012
The Xpert® MTB/RIF assay evaluation in South Korea, a country with an intermediate tuberculosis burden
1Department of Laboratory Medicine, Seoul National University Hospital, Seoul, South Korea.
Setting:
A central hospital laboratory in South Korea.
Objective:
To evaluate the usefulness of the Xpert® MTB/RIF assay in a country with an intermediate tuberculosis burden.
Design:
A total of 71 real-time polymerase chain reaction-positive sputum sediments were tested within 24 h by the Xpert MTB/RIF assay. Mycobacterium tuberculosis detection was compared with smear microscopy and culture. Rifampicin (RMP) resistance was compared with a culture-based method and rpoB gene sequencing. We also assessed the limit of detection for mutant proportions and time savings in diagnosis.
Results:
The Xpert MTB/RIF assay detected M. tuberculosis in 71 (100%) specimens (32 smear-positive, 39 smear-negative). This assay showed 100% (62/62) concordance with drug resistance confirmed by culture and 98.4% (61/62) concordance with sequencing. A specimen containing approximately 50% of mutant p.His526Tyr was falsely interpreted as wild-type bacilli by this assay. The minimal detection ratio was 5:1 of mutant vs. wild-type cells. The median time saved was 18.5 days (range 9-30) for the diagnosis of M. tuberculosis and 81.5 days (65-136) for RMP susceptibility in smear-negative, culture-positive patients.
Conclusions:
The Xpert MTB/RIF assay showed high sensitivity in detecting M. tuberculosis with information on RMP resistance, and had a more rapid time to diagnosis compared to conventional tests; however, the location and amount of mutation may affect test sensitivity.
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