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A Tuberculosis Molecular Bacterial Load Assay TB-MBLA
Published on: April 30, 2020
Evaluating the Cepheid Xpert TB/LTBI Research-Use-Only Assay for Detection of Active and Latent Mycobacterium
Brittney Sweetser1,2, Hoang Nguyen3, Hai Dang4
1Division of Pulmonary Diseases and Critical Care Medicine, University of California Irvine, Irvine, California, USA.
Background:
Accurate nonsputum tests are essential for improving tuberculosis (TB) detection. We report the first evaluation of the Xpert TB/LTBI assay (research-use-only; Cepheid, USA), which detects 9 Mycobacterium tuberculosis antigen-stimulated mRNA targets from blood.
Methods:
We enrolled individuals ≥12 years with presumptive TB from clinics in Uganda and Vietnam. All participants underwent sputum- (liquid culture; Xpert MTB/RIF Ultra) and blood-based (Xpert TB/LTBI; QuantiFERON-TB Gold Plus [QFT-Plus]) testing. Participants were classified as having active TB (positive sputum results), latent TB infection (LTBI; positive QFT-Plus with negative sputum results), or no TB infection. Diagnostic accuracy for active TB (primary analysis) and of a 2-step algorithm that first predicted TB infection (active TB or LTBI) and then distinguished active TB from LTBI was assessed using logistic regression and receiver operating characteristic analysis.
Results:
Among 214 participants included, 56.5% were male, 9.3% were with HIV, 29.0% had active TB, and 31.8% had LTBI. Xpert TB/LTBI area under the curve (AUC) was 0.92 (95% CI: .88-.96) for identifying active TB, and sensitivity was 93.5% (95% CI: 84.6-97.5) and specificity 76.3% (95% CI: 69.0-82.4) at a cut-point that achieved ≥90% sensitivity. In the 2-step algorithm, Xpert TB/LTBI had high accuracy for identifying TB infection in the first step, but accuracy was lower for distinguishing active TB from LTBI in the second step.
Conclusions:
Xpert TB/LTBI exceeded World Health Organization (WHO)-recommended minimum accuracy targets for a TB screening test. However, further refinement is needed to improve its ability to distinguish active TB from LTBI.
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