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Researchers Develop Improved Tuberculosis Test - 2003-04-08

A new, more effective test for tuberculosis is being developed by researchers, who say it would dramatically cut the time it takes to determine whether someone has the disease. The test would replace the TB skin test, which is one of the oldest diagnostic tools still used in modern medicine.

With the new, experimental TB test, doctors can find out the morning after blood is drawn whether someone has been exposed to the infectious lung disease, according to Ajit Lavani of Britain's Oxford University. Dr. Lalvani says the test, known as the Elispot, measures the presence of infection-fighting T-cells in the blood.

"The Elispot exploits the fact that TB induces a strong immune response by T-cells in the blood," said Professor Lavani, "and the Elispot detects and actually counts these T-cells directly from the blood sample."

In contrast, the old skin-prick test for diagnosing tuberculosis is notoriously unreliable. It detects the presence of antibodies, blood molecules that are activated by infection. Known as the tuberculin skin test, it does not tell doctors whether someone has been exposed to tuberculosis or has been vaccinated against the disease with BCG, a TB vaccine considered ineffective. BCG was once popular in Europe and many developing countries.

Professor Lalvani says the skin test's biggest shortcoming is that it may miss people with early stage tuberculosis who are infectious.

"These people appear completely normal, but they are carrying dormant or latent forms of the bacterium. And the only way we have of knowing whether they are infected or not until now has been this age-old skin test," he said.

Researcher Ajit Lalvani expects Elispot will become widely available throughout the developed world, where latent tuberculosis is more of a problem than the rest of the world.

But Professor Lalvani expects Elispot to be used in the developing world among people whose immune systems are weakened by HIV. Those individuals are thought to have played a major role in the resurgence of TB in recent years, since those with HIV are up to 10 times more likely to develop the infectious lung ailment.

Tuberculosis is responsible for more deaths than any other infectious illness, killing 2-3 million people each year.