New blood test to detect TB

Early results show the method of detecting TB by identifying a combination of telltale proteins – or biomarkers – in blood samples is up to 94% accurate, compared with the 40% to 60% accuracy of analysing sputum samples under a microscope in field conditions.

TB is the number one cause of death by infection in the world today killing about two million people. Yet most deaths from TB are easily preventable by early diagnosis and treatment.

The microscope sputum diagnostic test is most commonly used in developing countries, where there is a disproportionately high incidence of TB. As well as being unreliable, this test must often be repeated on three occasions to yield reliable results.

Currently, the new blood test uses an expensive tool known as ELISA to detect levels of biomarkers. Scientists aim to develop the method into a simple ‘dipstick’ test that will be cheap, accurate and produce quick results.

Professor Sanjeev Krishna, Professor of Molecular Parasitology and Medicine at St George’s, has been leading the research. He said: “We are putting forward a completely fresh approach to look at an ancient problem. I think it is going to be very exciting to make this work in clinics where a test for TB is desperately needed. The next stage will be to use the biomarkers we have identified to develop a cheap, accurate and rapid diagnostic test that can be used easily and quickly out in the field.”

About one-third of the world’s population carries the TB bacterium, Mycobacterium tuberculosis. A tenth of these will later develop the debilitating lung illness, often because their immune system is compromised by HIV infection or cancer.

“Improving diagnostic accuracy will have a massive impact on managing TB,” says Professor Krishna. Treatment is a lengthy, costly process: patients must take four different antibiotics for two months, followed by two antibiotic drugs for a further four months.

“If a clinic could rule out TB infection reliably using these types of tests, this would enable valuable resources to be targeted at the patients who need treatment,” Professor Krishna explains.

The initial results of the test were published in The Lancet last September.