New diagnostic test for latent tuberculosis introduced

The Tuberculin skin test, used to detect latent Mycobacterium tuberculosis infection, has many drawbacks and a new diagnostic test for latent tuberculosis (QuantiFERON®-TB) has recently been introduced.

This test measures the production of interferon- in whole blood upon stimulation with Purified Protein Derivative. The QuantiFERONT®-TB test addresses the operational problems with the tuberculin skin test, but as the test is based on Purified Protein Derivative it still has a low specificity in populations vaccinated with the BCG vaccine. Researchers have modified the test to include the antigens ESAT-6 and CFP-10 not present in BCG vaccine strains and the vast majority of non-tuberculous mycobacteria.

This test was used to detect infection in contacts in a tuberculosis outbreak at a Danish high school. The majority of the contacts were BCG-unvaccinated which allowed a direct comparison of the skin test and the novel blood test in individuals whose skin test was not confounded by vaccination. An excellent agreement between the two tests was found (94%, kappa value 0.866) and in contrast to the blood test based on Purified Protein Derivative the novel blood test was not influenced by the vaccination status of the subjects tested.

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