Diagnostic accuracy of the Cepheid MTB host response assay for the detection of pulmonary TB

TL;DR

This study evaluates a blood test for detecting pulmonary TB and finds it has high sensitivity but low specificity, making it unsuitable as a standalone diagnostic tool.

Contribution

The study provides new evidence on the diagnostic accuracy of the Xpert MTB Host Response blood test for pulmonary TB.

Findings

Xpert HR blood test showed 91% sensitivity and 45% specificity for detecting pulmonary TB.

The test's specificity was significantly lower among people living with HIV.

The test's performance varied by country, indicating potential contextual influences.

Abstract

Current sputum-based diagnostic approaches fail to identify some individuals with active TB, underscoring the need for tests that do not rely on sputum. This study assessed the diagnostic accuracy of the Xpert MTB Host Response (Xpert HR) blood test for detecting pulmonary TB.

We conducted a prospective study in adults with pulmonary TB symptoms who underwent Xpert HR testing. Diagnostic accuracy was assessed against a microbiological reference standard of sputum cultures and molecular testing.

Among 813 participants, 52% were female, median age was 38 years, and 192 (24%) were HIV-positive. For Xpert HR performed using capillary blood, sensitivity was 91% (95% confidence interval [CI]: 86–94), specificity was 45% (95% CI: 41–49), and area under the receiver operating characteristic curve was 0.85 (95% CI: 0.81–0.89). Country-specific differences in performance were observed. Sensitivity was 93% (95% CI: 76–98) and specificity was 18% (95% CI: 13–27) among people living with HIV.

The Xpert HR TB assay demonstrated promising sensitivity, but its specificity did not meet minimum target product profiles for a TB triage or case detection test. In its current form, Xpert HR cannot replace more sensitive nucleic acid amplification tests in sputum-productive individuals.

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