Pooled sputum testing cuts TB test costs while keeping high accuracy

Tuberculosis programs in high-burden, resource-constrained countries face a practical barrier: the cost of cartridges for the WHO recommended molecular test Xpert ® MTB/RIF Ultra (Xpert Ultra). To see whether testing multiple samples together could stretch resources without losing accuracy, a research team led by Sayera Banu evaluated pooled sputum testing in Bangladesh. Between July 2024 and February 2025, the study enrolled adults with presumptive pulmonary TB (PTB) from both healthcare facilities and urban slum communities, using facility-based and community-based case finding. Each participant provided two sputum samples: one used for individual and pooled Xpert Ultra testing, and another sent for culture, the microbiological reference standard. The study compared pooled and individual Xpert Ultra results against culture and also examined cartridge use to estimate cost savings. By designing the evaluation across primary and secondary care sites and community settings, the team aimed to reflect real-world conditions where diagnostic resources are limited and demand for rapid molecular testing is high. The question at the center of the work was straightforward: can pooling sputum maintain diagnostic performance while substantially reducing cartridge consumption and cost?

The diagnostic evaluation was prospective and multi-site. In total, 3,043 individuals were tested individually and also as part of 771 pooled samples. Results were compared to culture as the microbiological reference standard. Overall sensitivity for pooled Xpert Ultra was 85.8% (95% CI: 79.8-90.6), while individual Xpert Ultra sensitivity was 89.2% (83.7-93.4). Specificity was high for both approaches: pooled Xpert Ultra 98.9% (98.4-99.2) and individual Xpert Ultra 98.1% (97.5-98.6). The pooled approach detected 100% of the high, medium, and low burden categories that individual testing identified, but performance declined for very low bacterial loads (81.8%) and especially trace results (31.4%). The study also included a cost analysis based on cartridge usage: pooled testing reduced cartridge use and associated cost by 55.8% compared with individual testing. Throughout, the work used Xpert ® MTB/RIF Ultra (Xpert Ultra) as the molecular test under evaluation.

The findings show a clear trade-off that could favor pooled testing in many programmatic settings. Pooled sputum testing with Xpert Ultra offered diagnostic performance close to individual testing overall, while delivering a large reduction in cartridge use and cost. That makes pooled testing attractive for scaling up molecular TB diagnosis where cartridge cost is the limiting factor. At the same time, the weaker detection for very low and trace categories highlights an important limitation: some low-burden infections are less likely to be found when samples are pooled. Programs considering pooling will need to weigh the benefit of testing many more people against the risk of missing a subset of low-burden cases, and may choose pooling strategies based on local prevalence, the priorities of case finding, and the acceptability of that trade-off. In countries such as Bangladesh, the authors conclude pooled Xpert Ultra testing offers a practical, scalable option to expand access to rapid molecular diagnosis of pulmonary TB (PTB) in resource-limited, high-burden settings.