New TB Test May Help Simplify Diagnosis

Blood analysis distinguishes between active and latent disease, researchers say

By Robert Preidt

Friday, February 19, 2016

FRIDAY, Feb. 19, 2016 (HealthDay News) -- A simple new blood test for tuberculosis may one day help improve diagnosis and treatment of the deadly disease in developing countries, researchers report.

The inexpensive test identifies a gene expression "signature" that distinguishes people with active TB from those with either latent TB or other diseases, according to the research team from the Stanford University School of Medicine, in Palo Alto, Calif.

The work is outlined in a paper published online Feb. 19 in The Lancet Respiratory Medicine journal.

Each year, 9.6 million people worldwide are newly infected with TB, a bacterial infection that usually affects the lungs, and 1.5 million die from the difficult-to-diagnose disease, the researchers noted.

"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," assistant professor of medicine Purvesh Khatri said in a university news release. Khatri is the paper's senior author.

Older diagnostic methods -- such as skin prick testing and interferon assays (a type of blood test) -- can't distinguish between people with active TB and those who are no longer sick or have been vaccinated against the disease. The older tests also can miss TB in HIV patients, the researchers said.

Analysis of sputum coughed up by patients is a common way to check for TB, but it can be hard for people to produce sputum on demand, said paper first author Dr. Tim Sweeney.

He added that the sputum test is of little help in monitoring response to treatment. And, as patients start to get better, they often can't produce sputum for the test.

The new blood test eliminates the need to collect sputum, won't give a positive result if a person has latent TB or has had a TB vaccine, and can detect a TB infection even if a person has HIV, according to the researchers. They also say it's effective no matter the strain of TB or whether the strain is resistant to antibiotics. And, the test can be used in children and adults.

Khatri said more work is needed to develop the test for widespread use, and he has begun collecting funding for the process.

SOURCE: Stanford University, news release, Feb. 19, 2016

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