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Updated: Apr 24, 2026

Diagnosing Pulmonary Tuberculosis with the Xpert MTB/RIF Test
Published on: April 9, 2012
False-positive rifampicin resistance on Xpert® MTB/RIF caused by a silent mutation in the rpoB gene
V Mathys1, M van de Vyvere2, E de Droogh3
1National Reference Centre of Tuberculosis and Mycobacteria, Communicable and Infectious Diseases, Scientific Institute of Public Health, Brussels, Belgium.
Abstract:
The Xpert® MTB/RIF assay detects the presence of Mycobacterium tuberculosis and its resistance to rifampicin (RMP) directly in sputum samples. Discrepant results were observed in a case of smear-positive pulmonary tuberculosis that was Xpert-resistant but phenotypically susceptible to RMP. Complementary investigations (repeat Xpert, Genotype®MTBDRplus assay and sequencing of the rpoB gene) revealed the presence of a silent mutation in the rpoB gene, leading to the conclusion of a false-positive Xpert result. As misinterpretation of Xpert results may lead to inappropriate treatment, the presence of rpoB mutations should be confirmed by sequencing the rpoB gene.
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