Interferon-Gamma Release Tests Can Measure TB Exposure

Lack of sensitivity needs further investigation, however

FRIDAY, March 16 (HealthDay News) -- Interferon-gamma blood tests for tuberculosis correlate with exposure duration and helped identify customers of a Dutch supermarket exposed to an infected employee, according to a report in the March issue of the American Journal of Respiratory and Critical Care Medicine.

Ailko Bossink, M.D., Ph.D., of Diakonessenhuis Utrecht in the Netherlands, and colleagues compared the tuberculin skin test (TST), QuantiFERON- TB Gold (QFT-G) and T-SPOT.TB tests in 785 bacillus Calmette-Guérin unvaccinated contacts of a supermarket employee with smear-positive tuberculosis and correlated results with measures of recent exposure.

The investigators found that while TST results were associated with age, positive interferon-gamma responses were associated with cumulative shopping time. In participants having a TST of 15 mm or greater, the QFT-G and T-SPOT.TB sensitivities were 42.2 and 51.3 percent, respectively.

"Blood test results were associated with exposure, whereas the TST was not," the authors write. "A possible lack of sensitivity of interferon-gamma assays in detecting individuals with TST of 15 mm or greater, despite negative bacillus Calmette-Guérin vaccination status, warrants further investigation into alternative cutoff values."

Bossnik serves as an advisory board member for Oxford Immunotec, Ltd.

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