A new more reliable and quicker test for tuberculosis (TB) has been approved for use in Europe.
The T SPOT-TB blood test will replace the tuberculin skin test for TB which has been in use for the last century. The tuberculin test can be inaccurate yielding a large number of false positive and false negative results, and takes up to a week to provide a result. By contrast, the T SPOT-TB test can provide results overnight.
“Accurate testing is vital for effective [TB] control, especially with the threat of multi-drug resistant TB and the recent increase in the incidence of the disease hanging over us,” said Paul Sommerfield of the charity TB Alert.
"The tools we use to diagnose TB are 50-100 years old; this disease has been neglected for decades. I am pleased that we have finally brought the benefits of modern scientific research to the front-line to fight this age-old disease," commented Dr Ajit Lalvani of Oxford University, the scientist who has led the development of the test over the last ten years. "In contrast to the crude and inaccurate skin test, the new blood test is fast, accurate and convenient. It is a 100-year upgrade for diagnosing TB and I believe it will significantly improve the way we manage tuberculosis."
The T SPOT-TB blood test looks for T cells produced by the body in response to infection with TB. A total of 14 separate clinical trials have provided data on the efficacy of the T SPOT test.
Developed at Oxford University, the T SPOT-TB test can determine if an individual has been exposed to TB with greater accuracy than the tuberculin skin test.
A key selling point of the test is its ability to detect TB infection in HIV-positive individuals with weakened immune systems, claim the developers. TB is the commonest cause of death in people with AIDS around the world and approximately 200 cases of TB in HIV-positive individuals are seen in the UK every year.
The only study to look specifically at the performance of the test in HIV-positive individuals found that the test detected TB-specific T cells in 90% of 39 HIV-positive Zambian patients wth active TB confirmed by at least one smear-positive sputum sample; in comparison the PPD test detected 72% (a non-significant difference; Chapman 2002). However, the test's perfomance was considerably poorer when it came to detection of latent TB in HIV-positive individuals; it produced positive results in 43% of the HIV-positive sample, compared to a 36% positive rate for the tuberculin skin test. In HIV-negative individuals there was no significant difference in detection rates between the tuberculin skin test and the T SPOT TB test.
However the authors note that the decline in sensitivity in immunocompromised but asymptomatic individuals was lower for the T SPOT TB test than either the PPD or tuberculin skin test.
The magnitude of the advance in TB diagnosis for countries with high levels of HIV and TB infection is still in question, with the authors suggesting that larger scale trials need to take place.
Chapman ALN et al. Rapid detection of active and latent tuberculosis infection in HIV-positive individuals by enumeration of Mycobacterium tuberculosis-specific T-cells. AIDS 16: 2285-2293, 2002.