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Simple Blood Test Diagnoses People With Active TB

FILE - A physician examines an X-ray picture of a tuberculosis patient.
FILE - A physician examines an X-ray picture of a tuberculosis patient.

Each year, 9.6 million people become infected with tuberculosis; 1.5 million of them die. The rest silently carry the bacterium in a latent state, with the constant threat that it could become active TB.

It's estimated that one-third of the world's population is infected with TB, and the active cases are difficult to diagnose.

Purvesh Khatri, a computational immunologist who analyzes data on TB infections, says there are limitations to the current diagnostic test that uses sputum, which is coughed up from a person's respiratory tract.

While the test is highly accurate, it is hard to perform on some people.

"The problem is that it requires sputum, and the children cannot cough up sputum," Khatri said.

In addition, the traditional test can't distinguish patients with active TB from those who have recovered from tuberculosis and those who have received the BCG tuberculosis vaccine. Also, it can be hard to detect TB in those infected with the virus that causes AIDS.

New test

So, in 2014, the World Health Organization challenged researchers to develop a simple blood test to easily diagnose and sort out those who have latent disease from those who have active TB.

Khatri and his colleagues at Stanford University in California have done just that, creating a highly accurate blood test that could be performed in resource-poor countries where new infections are common.

When someone becomes infected with active TB, it sets off a chain reaction of activity in hundreds of genes. The blood test developed by Khatri and colleagues identifies three genes that respond in a consistent pattern when the disease becomes active.

In a study published in the journal Lancet Respiratory Medicine, the Stanford scientists report the results of the test in 1,400 blood samples. The test correctly diagnosed 86 percent of samples from children with active TB, and the test was accurate in 99 percent of cases where there was no active disease.

New possibilities

Khatri says the blood test may also be used in another way.

"We may be able to use this same [genetic] signature [to see] whether the patient is responding to treatment or not," he said.

Researchers next plan to conduct a clinical trial in Brazil to see how well the blood test works in the real world with people who have been exposed to tuberculosis.