A rapid, accurate test for tuberculosis could cut infection rates around the world, say experts.
Immune system cells respond to the bacteria
The T-SPOT test was more reliable than the century old Heaf test in trials in 4,000 patients and is approved for use in Europe and global TB hotspots.
Developed by scientists at Oxford University, it comes at a time when the World Health Organisation has declared TB a global emergency.
Experts said it would cut TB cases in just a few years.
Last week the British Thoracic Society warned there are about 3,000 cases of this respiratory disease in London each year - double the total of 15 years ago, and the number of cases in England and Wales is up 20% since 2002.
In the UK there are about 7,500 cases of TB each year and worldwide there are about nine million cases and two million deaths from TB each year.
A long course of antibiotics is usually sufficient to cure a patient, but the challenge is to identify those infected before they develop the full-blown disease.
If caught early in the latent stage, when the patient has no symptoms, it can be treated with one drug rather than four and its spread to others can be prevented.
People with active TB of the lung can infect around 10 to 15 other people just by coughing, sneezing or talking.
The traditional test for TB, known as the tuberculin skin test or Heaf test, has several shortcomings.
It can take three to five days to give a result and can give false-positive results in people who have been vaccinated against TB, or exposed to other similar types of microbes.
It is thought up to half of people given treatment for TB on the basis of a positive skin test to not have TB at all. Similarly, the test fails to detect half of people with latent TB.
False-negatives are particularly common in individuals with weakened immune systems, including young babies, people with HIV, transplant patients, the elderly and the homeless.
It is also unpleasant for the patient as it can result in blistering and scarring of the skin, and can be hard to interpret.
In comparison, Oxford Immunotec's T-SPOT TB test produces far fewer false results and is reliable, even in people with weakened immune systems and those who have been immunised against TB.
It is based on analysing blood samples for the presence of immune system cells that are activated by a protein produced by the TB bacterium, but not by any strains of the BCG vaccine.
Rapid and accurate
Only one standard blood sample is required and results are available the next morning.
Dr Ajit Lalvani who devised the test said: "The new blood test is fast, accurate and convenient.
"I believe it will significantly improve the way we manage tuberculosis. It will allow us to screen more widely and more effectively."
He said it would identify infected people missed by the skin test and allow treatment to be directed at those who really need it.
Although the new test is more expensive than the older methods, it would eventually reduce the higher costs
associated with treating TB patients, experts said.
Professor Peter Davis, director of the Tuberculosis Research and Resources Unit in Liverpool, said: "It will save a lot of angst, a lot of anxiety and a lot of money too."
Paul Sommerfeld, chair of TB Alert said: "Accurate testing is vital for effective disease control, especially with the threat of multi-drug resistant TB and the recent increase in incidence of the disease hanging over us."
"We are very excited that this could be an opportunity to radically change the strategy we have available to us to tackle TB across the world," he said.
The Department of Health is due to publish its TB action plan on how to tackle rising cases of the disease later this year or early next year.
A spokeswoman said: "The department welcomes the development of this new test which has the potential to help clarify TB diagnosis in some patients.
"Further work is needed before its role in routine TB diagnosis is confirmed."