Rapid Blood Test More Accurate than Tuberculin Skin Test

A study has shown that a rapid new assay for the diagnosis of tuberculosis is more accurate than the currently used tuberculin skin test.

Called ELISPOT (enzyme-linked immunospot), the new test differs from classical immunoassays by not being aimed directly at the infectious agent. Instead, it detects T-cells specific for Mycobacterium tuberculosis antigens that are absent from Mycobacterium bovis BCG (bacillus Calmette-guerin) and most environmental mycobacteria.

Investigators compared ELISPOT to the tuberculin test during an outbreak of tuberculosis at a school in Leicestershire, UK. They found after testing 535 students that although agreement between the tests was high (89% concordance), ELISPOT correlated significantly more closely with M tuberculosis exposure than did the tuberculin skin test on the basis of measures of proximity and duration of exposure to the index case. The tuberculin skin test was significantly more likely to be positive in BCG-vaccinated students than in nonvaccinated students, whereas ELISPOT results were not associated with BCG vaccination. ELISPOT was developed by researchers at the University of Oxford (UK). Their study was published in the April 5, 2003, issue of The Lancet.

Senior author Dr. Ajit Lalvani, a researcher in the department of clinical medicine at the university, explained, "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.”


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