Diagnostic Test Distinguishes Between Active and Latent Tuberculosis

An innovative blood test has been developed as an additional test to distinguish rapidly individuals with active tuberculosis (TB), and from these, those with latent TB infection.

By simply performing an extra blood test using a protein of the bacillus, Mycobacterium tuberculosis, named heparin-binding hemagglutinin adhesin (HBHA), it was possible to distinguish between those infected from those who have progressed to the pathological phase of the disease.

Scientists at the Catholic University of the Sacred Heart (Rome, Italy) developed the test in collaboration with others at the L. Spallanzani National Institute for Infectious Diseases (INMI; Rome, Italy). The team assayed the blood of 87 individuals at different stages of TB who scored positive with the QuantiFERON TB Gold In-Tube test (QFT-IT; Cellestis GmbH; Darmstadt, Germany). The QFT-IT blood test is an interferon-γ release assays (IGRA), based on the release of interferon-γ in response to M. tuberculosis-specific antigens, and is able to identify selectively those who have contracted TB infection.

In the study, the scientists developed an innovative diagnostic algorithm, which consists of a response to the protein HBHA in combination with the IGRA and the results have shown that the response to HBHA is associated with latent TB infection. This procedure allows the rapid identification those who really need the treatment for active TB. They showed that the lymphocyte T-cell response to a recombinant and methylated HBHA of M. tuberculosis produced in M. smegmatis--a nonpathogenic microorganism-- is useful to discriminate between active and nonactive TB disease among those responsive to QFT-IT in a whole blood system.

Stefania Zanetti, PhD, a professor of microbiology at the University of Sassari (Sassari, Italy), said," The response to HBHA can be used as a biomarkers for latent TB infection and then to some extent can be considered as a response of protection to TB. It is important to understand what are the mechanisms triggered by the infection which can cause the appearance or not of the disease.” The study was published online on March 29, 2011, in the Public Library of Science journal PLoS ONE.

Related Links:
Catholic University of the Sacred Heart
Italian National Institute for Infectious Diseases
Cellestis
University of Sassari