New Assay Efficacious for Diagnosing Extrapulmonary Tuberculosis and Rifampin Resistance

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Xpert sensitivity varies across different extrapulmonary specimens, while for most specimens, specificity is high, the test rarely yielding a positive result for people without TB.
Xpert sensitivity varies across different extrapulmonary specimens, while for most specimens, specificity is high, the test rarely yielding a positive result for people without TB.

Xpert MTB/RIF (Xpert®) may be helpful for confirming a diagnosis of extrapulmonary tuberculosis (TB), and can accurately detect resistance to rifampicin, according to study results published in the Cochrane Database of Systematic Reviews.

Xpert is an automated diagnostic test for detecting Mycobacterium tuberculosis complex, and the World Health Organization has updated its policy statement, which expands recommendations for the use of Xpert for pulmonary TB in adults and provides additional guidance for its use in extrapulmonary disease. In this review, the study investigators evaluated the accuracy of Xpert in diagnosing extrapulmonary TB and for rifampicin resistance in patients assumed to have extrapulmonary TB.

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A total of 66 studies that evaluated 16,213 specimens for detection of extrapulmonary TB and rifampicin resistance were included in this review. Pooled Xpert sensitivity varied considerably across the different types of specimens; 31% in pleural tissue to 97% in bone or joint fluid. The sensitivity was >80% in urine and bone as well as in joint fluid and tissue. Pooled specificity varied less than specificity, and was 82% in bone or joint tissue and 99% in pleural fluid and urine. Xpert specificity was ≥98% in cerebrospinal fluid, pleural fluid, urine, and peritoneal fluid.

For rifampin resistance, Xpert pooled sensitivity (20 studies; 148 specimens) demonstrated high-certainty evidence, with results of 95% (95% CI, 89.7% to 97.9%) and specificity (39 studies; 1088 specimens) of 98.7% (95% CI,97.8% to 99.4%), respectively.

“Xpert sensitivity varies across different extrapulmonary specimens, while for most specimens, specificity is high, the test rarely yielding a positive result for people without TB,” wrote the study authors.

Reference

Kohli M, Schiller I, Dendukuri N, Dheda K, Denkinger CM, Schumacher SG, Steingart KR. Xpert® MTB/RIF assay for extrapulmonary tuberculosis and rifampicin resistance. Cochrane Database Syst Rev. 2018;8:CD012768. doi:10.1002/14651858.CD012768.pub2

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