A new blood test that could transform tuberculosis diagnosis in developing countries

In 2014 the World Health Organization challenged researchers to develop better diagnostic tests for active TB.

WHO called for a test that would give a positive result at least 66 per cent of the time when a child has active TB. Researchers at the Stanford University School of Medicine in the US have now developed a new test for TB that is 86 per cent sensitive for detection of active TB in children. If the test result is negative then that result is correct in 99 per cent of cases.

The new test uses a blood sample and removes the need to collect sputum. It can differentiate between people who have had a TB vaccination or just have latent TB and those with active TB infection. The test works in adults as well as children.

The test uses polymerase chain reaction technology that until recently was only available in modern laboratories. However in recent times this technology has been simplified and made robust enough to function in small portable instruments that can even be solar powered rather than having to rely on a mains electricity supply. This makes such technology ideal for use in rural areas in developing countries where TB is still a common disease. The Stanford team identified three human genes whose expression changes in a consistent pattern when a person has an active TB infection and the test measures the expression of these three genes.

Globally, tuberculosis infects 9.6 million new patients each year and kills 1.5 million people. Yet the disease remains difficult to diagnose. "One-third of the world's population is currently infected with TB. Even if only 10 percent of them get active TB, that's still 3 percent of the world's population -- 240 million people," said Purvesh Khatri, PhD, assistant professor of medicine and senior author of the new study.

The Stanford team are now working on developing the test so that it can be used widely in areas of need, both to diagnose TB in patients and to monitor recovery in clinical trials, allowing for more rapid development of better and cheaper treatments.

Further reading:

Stanford Medicine News Center
Purvesh Khatri, PhD et al. Genome-wide expression for diagnosis of pulmonary tuberculosis: a multicohort analysis. Lancet Respiratory Medicine, February 2016

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