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Updated: Oct 15, 2025
Diagnosing Pulmonary Tuberculosis with the Xpert MTB/RIF Test
Published on: April 9, 2012
Need for caution when interpreting Xpert® MTB/RIF results for rifampin resistance among children
W Murithi1, E S Click2, K D McCarthy3
1Center for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya.
Insights
Xpert MTB/RIF testing in Kenyan children may falsely detect rifampin resistance, particularly with very low bacterial loads. Further research is needed to confirm this finding in pediatric tuberculosis diagnostics.
Area of Science:
- Pediatric Infectious Diseases
- Molecular Diagnostics
- Tuberculosis Research
Background:
- The World Health Organization recommends Xpert MTB/RIF as a primary diagnostic tool for childhood tuberculosis.
- Xpert MTB/RIF is extensively utilized globally, including in Kenya, for tuberculosis detection.
- Accurate diagnosis of tuberculosis in children is crucial for effective treatment and control.
Purpose of the Study:
- To evaluate the performance of Xpert MTB/RIF in diagnosing tuberculosis in children under five years old in Kenya.
- To investigate discrepancies in rifampin resistance detection between Xpert MTB/RIF and other diagnostic methods.
- To assess the clinical significance of potential false-positive rifampin resistance results.
Main Methods:
- A cohort of 300 HIV-positive and negative children under five years old was enrolled in Kisumu County, Kenya.
- Multiple specimen types were collected and tested using Xpert MTB/RIF, liquid culture, and phenotypic drug susceptibility testing (DST).
- Samples with detected rifampin resistance on Xpert underwent further testing with line-probe assay and sequencing.
Main Results:
- Of 32 children with confirmed tuberculosis, 27 tested positive by Xpert MTB/RIF.
- Xpert MTB/RIF detected rifampin resistance in 11% of positive cases, which was not confirmed by phenotypic DST, line-probe assay, or sequencing.
- False-positive rifampin resistance results on Xpert were associated with "very low" semi-quantitative readings and delayed or absent probe D signals.
Conclusions:
- The study suggests that Xpert MTB/RIF may yield false-positive results for rifampin resistance in pediatric specimens.
- Low bacterial load is a potential factor contributing to these false-positive findings.
- Further investigation is warranted to understand the implications of false rifampin resistance detection in pediatric TB management.
Abstract:
BACKGROUND: Recommended by the World Health Organization as an initial diagnostic test for TB in children, Xpert® MTB/RIF is widely implemented in many countries, including Kenya.METHODS: Three hundred HIV-positive and negative children (<5 years) were enrolled in Kisumu County, Kenya, from October 2013 to August 2015. Multiple specimen types were collected from each child and tested using Xpert, liquid culture, and phenotypic drug susceptibility testing (DST). Samples positive for rifampin (RIF) resistance on Xpert were tested using line-probe assay and sequencing.RESULTS: Of 32 children with bacteriologically confirmed TB, 27 had positive Xpert results. Of these, 3/27 (11%, 95% CI 4-28) had RIF resistance detected on Xpert, but not by phenotypic DST, line-probe assay, or sequencing. For these three children, five Xpert tests showed RIF resistance; all five tests had semi-quantitative "very low" results and delay or absence of probe D signal, whereas no Xpert results with higher semi-quantitative results showed RIF resistance. All three children responded well to standard TB treatment.CONCLUSIONS: False RIF resistance may be detected in pediatric specimens. Further study is needed to determine if false RIF resistance is associated with low bacterial load.
