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JAMA. 2005 Jun 8;293(22):2756-61.

Discrepancy between the tuberculin skin test and the whole-blood interferon gamma assay for the diagnosis of latent tuberculosis infection in an intermediate tuberculosis-burden country.

Author information

1
Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine and Lung Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.

Abstract

CONTEXT:

A recently developed whole-blood interferon gamma (IFN-gamma) assay based on stimulation with the Mycobacterium tuberculosis-specific antigens early secreted antigenic target 6 and culture filtrate protein 10 shows promise for the diagnosis of latent tuberculosis (TB) infection.

OBJECTIVE:

To compare the tuberculin skin test (TST) and the whole-blood IFN-gamma assay in the diagnosis of latent TB infection according to the intensity of exposure.

DESIGN AND SETTING:

A prospective comparison between the whole-blood IFN-gamma assay and the TST using a 2-TU dose of purified protein derivative RT23 in a population with intermediate TB burden was conducted sequentially between February 1, 2004, and February 28, 2005, in a Korean tertiary referral hospital.

PARTICIPANTS:

Of 273 participants, 220 (95.7%) had received BCG vaccine. Participants were grouped according to their risk of infection: group 1, no identifiable risk of M tuberculosis infection (n = 99); group 2, recent casual contacts (n = 72); group 3, recent close contacts (n = 48); group 4, bacteriologically or pathologically confirmed TB patients (n = 54).

MAIN OUTCOME MEASURES:

Levels of agreement between the TST and the IFN-gamma assay and the likelihood of infection in the various groups.

RESULTS:

For the TST with a 10-mm induration cutoff, the positive response rate in group 1 was 51%; group 2, 60%; group 3, 71%, and group 4, 78%. For the IFN-gamma assay, the positive response rate in group 1 was 4%; group 2, 10%; group 3, 44%; and group 4, 81%. The overall agreement between the TST and the IFN-gamma assay in healthy volunteers was kappa = 0.16. The odds of a positive test result per unit increase in exposure across the 4 groups increased by a factor of 5.31 (95% confidence interval [CI], 3.62-7.79) for the IFN-gamma assay and by a factor of 1.52 (95% CI, 1.20-1.91) for the TST (P<.001). Using a 15-mm induration cutoff for the TST did not make a substantial difference to the test results.

CONCLUSION:

The IFN-gamma assay is a better indicator of the risk of M tuberculosis infection than TST in a BCG-vaccinated population.

PMID:
15941805
DOI:
10.1001/jama.293.22.2756
[Indexed for MEDLINE]

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