Blood test could transform tuberculosis diagnosis

Blood test could transform tuberculosis diagnosis

Traditional diagnostic methods, such as the skin prick test and interferon assays, can't separate patients with active TB from those who are no longer sick or have merely been vaccinated against TB (and most countries vaccinate everyone against TB). These older diagnostics can miss a case of TB in patients with HIV.

Researchers at the Stanford University School of Medicine have identified a gene expression "signature" that distinguishes patients with active tuberculosis from those with either latent tuberculosis or other diseases.

A paper describing the work is published online in Lancet Respiratory Medicine.

The new test developed on an ordinary blood sample and removes the need to collect sputum. It can signal a TB infection even if the individual also has HIV. And it won't give a positive response if someone only has latent TB or has had a TB vaccine. It also doesn't matter which strain of TB has infected a person, or even if it has evolved resistance to antibiotic drugs. The test works in both adults and children.

WHO has called for a test that would give a positive result at least 66 percent of the time when a child has active TB. The test is 86 percent sensitive in children. And if the test comes up negative, it's right 99 percent of the time. That is, of 100 patients who test negative with the new test, 99 do not have active TB.

The requirements of the test are simple enough that it can potentially be done under relatively basic field conditions in rural and undeveloped areas of the world. Any hospital should be able to perform the test. Villages without electricity could likely use ordinary blood samples and a solar-powered PCR machine, which multiplies strands of DNA, to accurately test people for active TB.

When pathogens infect the cells of the body, the infection sets off a chain reaction that changes the expression of hundreds of human genes. The team identified three human genes whose expression changes in a consistent pattern, revealing the presence of an active tuberculosis infection.

The team validated the new three-gene test in a separate set of 1,400 human samples from 11 different data sets, confirming the diagnostic power of the test.

The new test not only accurately distinguishes patients who have active tuberculosis, it could also be used to monitor patients to see if they are getting better and how well they are responding to different treatments. Thus, it can be used not only for diagnosis and to inform treatment, but also to study the effectiveness of different treatments. The test's hugely accurate negative response would be especially helpful in monitoring the effectiveness of treatments during clinical trials.

http://med.stanford.edu/news/all-news/2016/02/blood-test-could-transform-tuberculosis-diagnosis-treatment.html

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