[Critical approach to the use of blood tests measuring gamma-interferon when suspecting active tuberculosis: clinical cases].

Assays measuring gamma-interferon (INGA) produced by peripheral lymphocytes exposed to antigens specific of Mycobacterium tuberculosis have a very high specificity, thus avoiding false positive results of the tuberculin skin test (TST) such as the BCG or atypical mycobacteria, and allowing a better targeting of treatments for latent tuberculosis infection (LTBI). Their sensitivity is superior to that of the TST in immuno-compromised and elderly subjects, and probably in immuno-competent individuals. They do not allow however to make the distinction between LTBI and active tuberculosis. Furthermore, their sensitivity, although superior to that of the TST, is not sufficient to exclude active TB specially in immuno-compromised subjects. Their main indication remains the detection of LTBI in screening or contact tracing, or in immuno-compromised subjects.