Tuberculosis (TB) is an infeccious disease usually caused by Micobacterium tuberculosis. Although the ethiological agent of tuberculosis was isolated in 1882, this disease is still a major public health issue in many countries. In 1993 it was even considered a global emergency by WHO. In intermediate/low incidence countries, as is the case of Portugal, the strategy for the elimination of TB involves not only the diagnosis and complete treatment of active disease cases, but it is also important to identify and treat cases of latent tuberculosis infection (LTBI). Until recently, the only test used in the diagnosis of LTBI was the tuberculin skin test (TST). Since 2001 and in Portugal since 2007, other tests began being used, namely “interferon gamma release assay” (IGRA). In this dissertation, is made an epidemiological analysis of TB in Portugal and worldwide. The interest of the diagnosis of eligible cases for LTBI treatment is approached, by making a comparative reference between existing tests - TST and IGRA. The results of the 7854 IGRA tests performed in the Micobacteriology Laboratory of Oporto Pulmonology Diagnostic Center, carried out from January 1, 2011 to December 31, 2013, in different population groups are analysed by comparing them with the results of previous TST, evaluating their impact on the selection of eligible individuals for LTBI treatment. From the analysis of the tests evaluated in the context of contact tracing, we conclude that the IGRA tests in conjunction with TST, avoided 51,5% of treatments for LTBI in the group of recent and close contacts and 67,1% in healthcare professionals. In groups with high susceptibility as are the cases of children under 5 years old and people infected with HIV, 1,3% and 7,2% were eligible for LTBI treatment respectively, more than would be if they had just made the TST.