This study showed that the new rapid blood test, developed by Ajit Lalvani and colleagues at the University of Oxford, UK, is more effective than the century-old skin-prick test for diagnosing TB infection. It enables doctors to screen people who have been in contact with an infectious TB sufferer and reliably identify those who are infected long before they actually develop the disease.
Diagnosis and preventative treatment of people with early TB infection before they develop disease (active tuberculosis) is essential for TB control. The existing skin test for diagnosing early infection is inconvenient, takes 3 to 7 days before it can be read and gives false-positive results in people vaccinated with BCG; the new test is easy, rapid, and not confounded by BCG vaccination.
Application of the blood test, known as ELISPOT, in the TB outbreak in a school in Leicestershire, UK, confirms that it is set to supersede the skin test as the primary diagnostic test for TB infection. Working closely with Leicestershire Health Authority and the staff and students at the school, the investigators used the new test to investigate the outbreak and offer the best possible management to the children at risk of infection. Children who were more exposed to the student with full-blown TB (in terms of physical proximity and duration of exposure, such as children from the same class or school year) were much more likely to test positive with ELISPOT than with the skin test.
The ELISPOT works in a unique way. Whereas conventional diagnostic tests rely on detecting antibodies induced by an infection, such antibodies are not generated by TB infection, which is why there has been no blood test until now. TB infection induces a strong response by immune cells in the blood called T-cells. It is these T-cells which are detected by the ELISPOT blood test.
Ajit Lalvani comments: "These results have important implications for future control of a disease whose incidence has seen a marked increase in recent years. Improvements in the early diagnosis of TB infection will enable more people to be treated while their infection is still dormant, thus preventing them from developing full-blown TB which is highly infectious to others. Our results definitively confirmed that the ELISPOT test is more accurate than the skin test-this means that the ELISPOT test is set to supersede the skin test and improve the control and prevention of this resurgent disease."
Contact: Dr Ajit Lalvani, Nuffield Department of Clinical Medicine,
University of Oxford Level 7, John Radcliffe Hospital, Headley Way,
OXFORD OX3 9DU UK;
T) 44-186-522-1331;
F) 44-186-522-1331;
E)
ajit.lalvani@ndm.ox.ac.uk
Journal
The Lancet