ELISPOT May Be a Major Advance in TB Screening

Laurie Barclay, MD

April 3, 2003 — ELISPOT, an enzyme-linked immunospot that detects T cells specific for Mycobacterium tuberculosis antigens, promises to be a major advance in screening for tuberculosis (TB), according to the results of a study published in the April 5 issue of The Lancet. In a comparison trial, ELISPOT was more accurate than the tuberculin skin test and was unaffected by BCG vaccination.

"The advances in molecular medicine in recent years have yet to result in any significant improvement in how we diagnose and manage TB patients and their contacts, and the diagnosis of early TB infection still relies on the 100-year-old tuberculin skin test," senior author Ajit Lalvani, from the University of Oxford, U.K., says in a news release. "This new test is the first diagnostic test in medicine to work by detecting T cells rather than antibodies."

Dr. Lalvani's group tested 535 students at a school in Leicestershire, U.K., where one infectious index case resulted in a large TB outbreak. Concordance between the tuberculin skin test and ELISPOT was 89% (P < .0001). However, children were significantly more likely to test positive with ELISPOT than with the skin test when they had greater physical proximity (P = .03) and duration of exposure (P = .007) to the index case.

Although the tuberculin test was more likely to be positive in children who had been vaccinated with BCG (P = .002), ELISPOT results did not correlate with BCG vaccination.

"We worked closely with the school and the local health authority in the midst of the outbreak to improve diagnosis for students at risk of TB infection," Dr. Lalvani says. "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."

The authors suggest that improvements in the early diagnosis of TB will facilitate identification and treatment of more people with latent TB. "Although the tuberculin skin test is cheap, related indirect costs are associated with return visits and the trained staff required to administer and read the test," they write. "Introduction of ELISPOT might initially increase the cost of TB control, but the savings that would follow from improved diagnosis of latent TB infection could make it very cost-effective in the long term."

Dr. Lalvani is the named inventor on several patents related to T cell-based diagnosis fields by the University of Oxford.

Lancet. 2003;361:1168-1173

Reviewed by Gary D. Vogin, MD