Assessment of the Xpert assay among adult pulmonary tuberculosis suspects with and without diabetes mellitus

SETTING: Pune and Pimpri-Chinchwad Municipal Corporation area, Maharashtra State, India.

OBJECTIVE: To assess the sensitivity and specificity of the Xpert^® MTB/RIF assay among adults with suspected pulmonary tuberculosis (PTB) and with or without diabetes (DM).

DESIGN: As part of a prospective cohort study, we screened 2359 adults presumed to have PTB with no history of TB. All individuals underwent testing for two sputum smears, culture, Xpert, glycated haemoglobin and fasting blood sugar. We calculated sensitivity and specificity of Xpert by comparing it with TB sputum culture result as a gold standard.

RESULTS: Among screened individuals, 483 (20%) were diagnosed with DM and 1153 (49%) with pre-DM; 723 (31%) had no DM. Overall sensitivity of Xpert was 96% (95%CI 95-97) and specificity was 91% (95%CI 89-93). Xpert sensitivity was significantly higher among DM group (98%) than in the ‘No DM’ (95%; P < 0.01) and pre-DM (96%; P < 0.05) groups. Among sputum smear-negative individuals, Xpert sensitivity was higher in the DM group than in the No DM (92% vs. 82%; P = 0.054) and pre-DM group (92% vs. 82%; P = 0.037).

CONCLUSION: High sensitivity and specificity of Xpert underscores the need for its rapid scale up for the early detection of TB in settings with a high dual burden of TB and DM.

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