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Test Provides Good Specificity for Latent Tuberculosis

Interferon-γ-release assays offer high specificity in those with bacille Calmette-Guerin vaccination

MONDAY, July 7 (HealthDay News) -- Interferon-γ-release assays (IGRAs) and tuberculin skin tests both offer high specificity for tuberculosis in populations unvaccinated with bacille Calmette-Guerin, but the IGRAs also offer high specificity in those who are vaccinated, according to research published in the Aug. 5 issue of the Annals of Internal Medicine.

Madhukar Pai, M.D., Ph.D., of McGill University in Montreal, Quebec, Canada, and colleagues conducted a meta-analysis of 38 studies to assess the use of IGRAs for diagnosing latent tuberculosis infection.

The pooled sensitivity for QuantiFERON-TB Gold was 78 percent, for QuantiFERON-TB Gold In-Tube was 70 percent, and for T-SPOT.TB was 90 percent, the researchers report. The pooled specificity for the QuantiFERON tests was 99 percent in non-bacille Calmette-Guerin (BCG)-vaccinated subjects and 96 percent in subjects with the vaccination. Pooled specificity of T-SPOT.TB and its precommercial version ELISpot was 93 percent. Specificity for the skin test in BCG-vaccinated populations was low and very variable, the report indicates.

"Our results confirm that IGRAs have excellent specificity that is unaffected by BCG vaccination. In particular, we found that both QuantiFERON tests have excellent specificity on the basis of a large number of consistent studies," the authors write. "Our results suggest that tuberculin skin test specificity is high in non-BCG-vaccinated populations but low and highly variable in BCG-vaccinated populations. Overall, the high specificity of IGRAs, especially QuantiFERON, might prove to be useful in BCG-vaccinated individuals, particularly in settings where tuberculin skin test specificity is compromised by BCG vaccination after infancy or by multiple BCG vaccinations."

Pai consults for a non-profit that works with industry partners on diagnostics for neglected infectious diseases.

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