Pooling samples could expand TB testing worldwide

Testing sputum samples in small groups could nearly double access to rapid tuberculosis diagnosis without doubling costs. The largest study of pooled TB testing found that the approach cut molecular test cartridge use by 51%, helping inform new WHO guidance for resource-constrained settings.

The findings were generated by the largest ever study of “pooled” tuberculosis TB testing, carried out by Start4All, a four-year Unitaid-funded partnership led by LSTM with the Stop TB Partnership and research partners in seven high TB burden countries.

The study found that pooled sputum testing, examining samples from several people in a single molecular test cartridge, halves the number of cartridges needed to make successful diagnoses.

The research team’s paper on the performance and costs of pooled testing for molecular detection of TB has been published in The Lancet Global Health.

The study’s first author Dr Tushar Garg said the findings “demonstrate that the technique could increase access to accurate, rapid and low-cost TB testing, enabling thousands more people to be diagnosed around the globe”.

Informing WHO guidelines

The findings directly informed World Health Organization guidelines on pooled testing issued earlier this year, which recommended the technique for adolescents and adults in resource-constrained settings.

Dr Tom Wingfield, deputy director of LSTM’s Centre for Tuberculosis Research and chief investigator on Start4All, said: “This is the evidence that took pooled testing from a promising idea to a WHO recommendation, and it comes from routine laboratories and clinics in the countries that need it most, not from a research setting.

“Pooling needs no new technology. It makes smarter use of the machines and cartridges laboratories already have, so that many more people can receive a rapid molecular test from the same budget. That is what reaching the missed millions looks like in practice.”

Large-scale study

Between November 2023 and February 2025 more than 14,000 people with symptoms of TB in Bangladesh, Brazil, Cameroon, Kenya, Malawi, Nigeria and Vietnam took part in the study, through screening in communities and at primary health centres and district hospitals. Each person’s sputum was tested on its own and again as part of a pool of up to four specimens on Xpert MTB/RIF Ultra, the most widely used rapid molecular TB test.

The study is the first to measure pooled testing against culture, the reference standard for TB diagnosis, rather than only against individual molecular testing.

Pooled testing used just over 7,000 cartridges instead of the roughly 14,000 that individual testing required, a 51% reduction, cutting the cost of each test from nearly US$8 to less than US$4.

There was a slight drop of 3.1% in sensitivity (the number of people with TB correctly identified) of pooled testing compared to individual testing, which was mostly in specimens containing a very low TB bacterial load.

Cyrille Mbuli, a researcher from the Bamenda Center for Health Promotion and Research, the collaborating partner of Start4All in Cameroon, said: “The TB programmes have been asking a simple question: what do we give up when we pool tests, and what do we gain?

“The Start4All results confirm what our laboratories have seen: pooling lets us test almost twice as many people for the same investment.”

Deadliest single infection

Global efforts to tackle TB – the deadliest single infection which kills around 1.3 million people a year – are hampered by the large number who remain undiagnosed, untreated and unknowingly spreading TB in their homes and communities.

Chronic underinvestment has led to limited and inequitable access to WHO-recommended molecular rapid diagnostic tests, which only one-in-two people globally receive as their initial test.

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This research is already having a real-world impact in communities around the world through the creation of a new toolkit for healthcare professionals and National TB Programmes and a test cost calculator and decision developed by Stop TB Partnership.

The paper is one of a series of Start4All outputs on pooled testing:

• an explanation of the role of pooled sputum testing in the global TB diagnostic landscape, published in The Lancet Respiratory Medicine;
• a multicountry qualitative study in BMJ Open, led by Dr Vibol Iem at LSTM, found that laboratory staff, programme managers and people with TB in the seven countries considered pooled sputum testing feasible and acceptable;
• a cross-sectional study in Clinical Microbiology and Infection reported the diagnostic accuracy and potential resource savings of pooled testing among adults in Vietnam.

In the next phase of Start4All, pooled testing will be combined with computer-aided chest X-ray triage and expanded to tongue swab specimens, supporting simpler and scalable approaches that can expand access to molecular TB testing.