Pooled Xpert MTB/RIF Ultra testing shows high specificity but reduced sensitivity compared to individual testing in Vietnamese adults with presumptive tuberculosis.
Photo by Wengang Zhai / Unsplash
Key Takeaway
Note that pooled Xpert testing reduces costs but lowers sensitivity compared to individual testing in adults with presumptive TB.
This cross-sectional study assessed the diagnostic accuracy and resource efficiency of a pooled testing algorithm versus individual Xpert MTB/RIF Ultra testing. The analysis included 2,396 adults aged 15 years or older with presumptive tuberculosis across facility-based and community-based case-finding settings in Vietnam. Sputum specimens from multiple individuals were tested in pools, with individual testing performed only on positive pools.
Pooled testing yielded a sensitivity of 82.4% (95% CI: 77.9-86.3) and a specificity of 98.5% (95% CI: 97.8-99.0) against culture as the reference. In contrast, individual Xpert MTB/RIF Ultra testing showed a sensitivity of 86.5% (95% CI: 82.4-89.9) and a specificity of 98.1% (95% CI: 97.4-98.7). Sensitivity for pooled testing varied by setting, ranging from 59.1% in community-based case finding to 84.0% in facility-based case finding.
The study reported a 46.5% reduction in overall cartridge use and cost savings of USD 14,447. No adverse events, serious adverse events, discontinuations, or tolerability issues were reported. However, the sensitivity of pooled testing was notably lower than individual testing, particularly for paucibacillary disease. These limitations highlight the trade-off between resource efficiency and diagnostic sensitivity.
The findings suggest that pooled testing may be resource-efficient for TB screening in Vietnam, but context-specific implementation is essential. Clinicians must weigh the significant cartridge savings against the risk of reduced sensitivity when considering this strategy for presumptive cases.
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View Original Abstract ↓
ObjectivesA pooled testing algorithm for tuberculosis (TB), in which sputum specimens from multiple individuals are tested in pools with individual testing of positive pools, can optimise diagnostic resources. This study evaluated the diagnostic accuracy and cartridge savings of pooled testing with the Xpert MTB/RIF Ultra assay (Xpert-Ultra) relative to individual Xpert-Ultra testing.
MethodsWe conducted a cross-sectional study among 2,396 adults ([≥]15 years) with presumptive TB enrolled between July 2024 and February 2025, through facility-based case finding (FBCF) and community-based case finding (CBCF). Participants submitted two sputum specimens. The first underwent individual Xpert-Ultra testing; remnant specimens were combined into four-specimen pools and tested again with Xpert-Ultra. The second specimen was used to inoculate liquid culture (BACTEC MGIT). Data were used to simulate an up-front pooled testing strategy; sensitivity and specificity of this approach was estimated against culture, and cartridge use was compared with individual Xpert-Ultra testing.
ResultsOf 2,396 participants, 395 (16.5%) had a positive Xpert-Ultra and/or culture, including 360/912 (39.5%) in FBCF and 35/1484 (2.4%) in CBCF. The pooled testing approach had sensitivity of 82.4% (95% confidence interval [CI], 77.9-86.3) and specificity of 98.5% (97.8-99.0) compared to culture, with lower sensitivity than individual Xpert-Ultra testing (86.5%, 82.4-89.9) but high specificity (98.1%, 97.4-98.7). Sensitivity of pooled testing was lower in CBCF (59.1%, 36.4-79.3) than in FBCF (84.0%, 79.5-87), whereas cartridge savings were greater in CBCF (69.1% vs 9.6%). The pooling strategy reduced Xpert-Ultra cartridge use by 46.5%, saving USD 14,447.
ConclusionsPooled Xpert-Ultra testing among adults appears resource-efficient for TB screening in Vietnam. As sensitivity is lower compared to individual Xpert-Ultra testing, particularly for paucibacillary disease, these losses should be carefully weighed against gains in affordability and expand access to molecular testing. Careful, context-specific implementation is essential to maximise programmatic benefit while minimising missed persons with TB.
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