Chapter 4: Diagnosis of tuberculosis infection

Abstract

• The primary goal of testing for tuberculosis infection is to identify individuals who are at increased risk for the development of tuberculosis disease and who therefore would benefit from tuberculosis preventive treatment. • Testing for tuberculosis infection is NOT recommended in the following situations: ○ In persons who have a low risk of infection and if infected; ○ To support a tuberculosis disease diagnosis in adults and adolescents >12 years of age; ○ For routine mass screening of individuals outside of contact investigations or occupational screening programs; and ○ For the monitoring of tuberculosis disease treatment response. • Both the tuberculin skin test and interferon-gamma release assay are acceptable alternatives for tuberculosis infection diagnosis. Either test can be used for tuberculosis infection screening in any of the situations in which testing is indicated. However, there are preferences and exceptions: ○ An interferon-gamma release assay is the preferred test when: ○ children over two years of age and less than 10 years of age previously received a Bacille Calmette-Guérin (BCG) vaccine against tuberculosis; ○ persons at least 10 years of age received a BCG vaccine after infancy (older than one year of age), or received a BCG vaccine more than once and/or are uncertain about when they received a BCG vaccine; ○ adequate training and quality assessment and control are NOT available for tuberculin skin test administration and/or reading, but personnel and facilities to perform interferon-gamma release assays are available; ○ a person is unable or unlikely to return to have their tuberculin skin test read; or ○ tuberculin skin testing is contraindicated. ○ The tuberculin skin test is the preferred test when serial testing is planned to assess risk of new infection (ie, conversions). This includes repeat testing in a contact investigation, or serial testing of health care workers or other populations (eg, corrections staff or prison inmates) with potential for ongoing exposure. In these situations, interferon-gamma release assays are not acceptable. • Both tuberculosis infection diagnostic tests may be used sequentially in the following situations: ○ If either the tuberculin skin test or interferon-gamma release assay are negative, the other test may be used to increase sensitivity if the risk for infection is high, the risk for progression to tuberculosis disease is elevated, the risk for a poor outcome from tuberculosis disease is high and/or a person has conditions or habits that may reduce the sensitivity of the test. ○ If the initial tuberculin skin test is positive, but the likelihood of tuberculosis infection is low, or risk of a false positive result due to BCG is high, then an interferon-gamma release assay may be used to increase specificity. • When interpreting a tuberculosis infection diagnostic test result and considering whether someone is at risk of developing tuberculosis disease and would likely benefit from tuberculosis preventive treatment, the diagnostic test result should be considered in light of other factors, including the pretest probability for the person being truly infected, the individual risk of developing tuberculosis disease and the ability of the test to identify persons at risk of tuberculosis disease (ie, predictive value). Online tools exist to support this interpretation.