 Tuberculosis is a current infection during anti TNF therapy. After infectious contact, some patients will develop tuberculosis and some will only be infected without symptoms, they have Latent Tuberculosis Infection LTBI wich can reactivate later. In order to prevent this tuberculosis reactivation, LTBI diagnosis screening is preconised in patients who need anti TNF therapy. This diagnosis is made till now by the tuberculin skin test TST but this test is not specific of TB. New blood tests QFTB-G and T-SPOT.TB specific to MTB infection are now available. 