Blood Test Indicates Patients That May Develop Active TB

A new blood test can reveal which patients could develop active tuberculosis (TB) much more precisely than the 100-year old skin test.

Called ELISpot, the test works by detecting a protein signal, known as interferon-gamma, released by white blood cells of the immune system in response to TB infection. The test has been recommended for use alongside the skin test in around 20 countries worldwide, including the EU and North America.

The study that took place in Istanbul, Turkey, looked at children who had been exposed to TB at home. Children with a positive ELISpot blood test result had approximately a four-fold higher risk of developing TB disease than children with a negative result did. A higher proportion of children with a positive ELISpot blood test result developed TB disease compared to children with a positive TB skin test.

Professor Ajit Lalvani, the lead author of the study and a Wellcome Trust Senior Clinical Research Fellow at the Center for Respiratory Infection at Imperial College London (UK), said, "A lot of people in places like the UK think of TB as being an old disease that we no longer need to worry about, but even in this country the numbers of cases have been rising for almost 20 years. Outside the developed world, TB has reached pandemic proportions and it still causes an immense amount of suffering and death.

"Our study shows that new tools like the blood test can help tackle the global pandemic. We now know that the blood test really helps to target treatment to those who most need it in order to prevent them from developing active TB. Building on this work, we are now validating a next generation of tests that have been developed by our TB Task Force at Imperial," added Professor Lalvani.

The study appeared in the October 2008 journal Annals of Internal Medicine.

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