Researchers have developed a new blood test that can more accurately predict the development of tuberculosis (TB) up to two years before its onset in high-risk patients.

The new test predicts TB particularly in people living with persons having active TB -- a condition when the immune system is unable to stop the bacteria from growing. The blood test works by measuring the expression levels of four genes signature in the blood known as "RISK4" -- a combination of four genes associated with inflammatory responses.

"We found that this prediction (up to two years before the onset of the disease) is possible through measurements of a combination of a four-gene signature in the blood," said lead author Gerhard Walzl, Professor at the Stellenbosch University in South Africa. While "an individual component of this signature may not be sufficient to deliver an accurate diagnosis of prediction, but a combination of these markers improves its accuracy," Walzl added. The new test also predicts the development of TB without putting large numbers of lower-risk people through unnecessary preventative treatment.

The findings were published in the American Journal of Respiratory and Critical Care Medicine. Focusing on people who lived with someone with active TB, the research team enrolled 4,466 HIV-negative participants and took their blood samples. "We are hoping that primary health clinics will be able to use such a test and the reagents would then be readily available in that format, similar to the tests that are currently used to diagnose TB," Walzl noted.

Tuberculosis, caused by infection with Myobacterium tuberculosis (M.tb), is the world's leading cause of death brought on by a single pathogen. More than 10 million new cases of TB are diagnosed each year, and almost two million people die from the disease. Globally, 1.7 billion people are estimated to be infected with M.tb.