Advances in the diagnosis of tuberculosis infection

Abstract

One-third of the world-wide population currently presents latent tuberculosis infection (LTI). In Spain, TB is situated as the third disease of mandatory notification. The standard technique for the diagnosis of ITL is the tuberculin test (PPD), although its most important drawback is its specificity since the proteins used are not specific for Mycobacterium tuberculosis. In recent years, research has been done and new diagnostic methods have been approved based on the in vitro quantification of the immune cell response, the so-called interferon gamma release assays (IGRA). Compared with PPD, the main difference is that IGRAs detect the release of interferon-gamma in response to specific tuberculous antigens. In the absence of a true reference test for the diagnosis of tuberculosis infection, it is difficult to establish the sensitivity and specificity of these new diagnostic techniques. IGRAs have been used in the detection of ITL in subjects with immune system alterations (HIV, EEI, IRC, rheumatologic diseases) with good results. They are also being extensively used in the study of contacts. In recent studies involving serial controls of said tests, they were observed to present conversions and reversions that occur after exposure to M. tuberculosis. Today and with the current knowledge, it seems that IGRAs can complement PPD, but not substitute them.