Canadian Tuberculosis Standards

Également disponible en français sous le titre : Normes canadiennes pour la lutte antituberculeuse, 7 ième édition To obtain additional copies, please contact: This publication can be made available in alternative formats upon request. This publication may be reproduced for personal or internal use only without permission provided the source is fully acknowledged. • The goal of testing for latent tuberculosis infection (LTBI) is to identify individuals who are at increased risk for the development of active tuberculosis (TB) and therefore would benefit from treatment of LTBI. • Only those who would benefit from treatment should be tested, so a decision to test presupposes a decision to treat if the test is positive. • There are two accepted tests for identification of LTBI: the tuberculin skin test (TST) and the interferon gamma release assay (IGRA). • When interpreting a positive TST, it is important to consider much more than simply the size of the reaction. Rather, the TST should be considered according to three dimensions: size of induration, positive predictive value and risk of disease if the person is truly infected. • As with the TST, IGRAs are surrogate markers of Mycobacterium tuberculosis infection and indicate a cellular immune response to M. tuberculosis. • In general, IGRAs are more specific than the TST in populations vaccinated with Bacille Calmette-Guérin (BCG), especially if BCG is given after infancy or multiple times. • Neither the TST nor IGRAs can separate LTBI from TB disease and therefore have no value for active TB detection. Both tests have suboptimal sensitivity in active TB, especially in HIV-infected people and children. • Both tests appear to correlate well with the gradient of exposure. Both tests are associated with nonspecific variations and reproducibility issues, and borderline values need careful interpretation. • Neither IGRAs nor the TST have high accuracy for the prediction of active TB, although use of IGRAs might reduce the number of people considered for preventive treatment. 3 | CANADIAN TUBERCULOSIS STANDARDS – 7 TH EDITION MAJOR RECOMMENDATIONS Both the TST and IGRA are acceptable alternatives for LTBI diagnosis. Either test can be used for LTBI screening in any of the situations in which testing is indicated, with preferences and exceptions noted below. 1. Situations in which neither TST nor IGRAs should be used for testing • Neither the TST nor the IGRA should be used for testing people who have a low risk of …