Related Experiment Video
Updated: Sep 26, 2026
Diagnosing Pulmonary Tuberculosis with the Xpert MTB/RIF Test
Published on: April 9, 2012
Diagnostic performance and testing costs of pooled testing for molecular detection of tuberculosis in seven
Tushar Garg1, Melissa Sander2, Rachel L Byrne3
1Stop TB Partnership, Geneva, Switzerland.
Background:
Globally in 2024, only 54% of people diagnosed with tuberculosis received an initial WHO-recommended rapid molecular diagnostic test. Pooled testing could expand access to molecular detection using existing laboratory capacity. We aimed to evaluate the performance of pooled tuberculosis testing in a multicentre diagnostic accuracy study.
Methods:
In this prospective diagnostic accuracy study, we enrolled individuals with presumptive tuberculosis through facility-based case finding (district hospitals and primary health centres) and community-based case finding in Bangladesh, Brazil, Cameroon, Kenya, Malawi, Nigeria, and Viet Nam between Nov 30, 2023, and Feb 27, 2025. Sputum was tested individually on Xpert MTB/RIF Ultra (Xpert Ultra) and in pools of two, three, or four specimens on Xpert Ultra. Culture was used as the microbiological reference standard. We estimated the sensitivity and specificity of pooled testing versus culture, positive percent agreement (PPA) versus individual Xpert Ultra, and cartridge savings.
Findings:
Results were available for 14 040 (95·2%) participants from 3666 pools, including 3195 (87·2%) pools of four. Using culture as the reference standard, sensitivity of pooled testing versus individual Xpert Ultra was 84·9% (95% CI 82·5-87·0) versus 88·0% (85·9-90·0), and specificity was 98·3% (98·0-98·5) versus 97·7% (97·4-97·9). PPA was 90·1% (95% CI 88·4-91·7), remaining above 96% for high (98·1% [96·1-99·2]), medium (98·3% [95·8-99·5]), and low (96·5% [93·8-98·2]) individual Xpert Ultra semiquantitative grades, but lower for very low (86·6% [79·9-91·7]) and trace (55·4% [47·9-62·7]) grades. Pooled testing used 7028 cartridges versus 14 362 for individual testing, a 51·1% reduction.
Interpretation:
Pooled testing with Xpert Ultra had slightly higher specificity and a 3·2 percentage points lower sensitivity compared with individual Xpert Ultra, and required half the cartridge use. Scale-up of this approach could facilitate expanded access to molecular testing in low to moderate tuberculosis positivity settings without the need for additional infrastructure.
Funding:
Unitaid.
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