The primary goal of testing for TB infection is to identify individuals who are at increased risk for the development of TB disease and therefore may benefit from treatment of TB infection to prevent TB disease (often referred to as tuberculosis preventive treatment [TPT]). In some situations, testing for TB infection is performed among individuals at increased risk of TB exposure, those who regularly interact with vulnerable populations, or who may be at increased risk of adverse outcomes should TB disease develop.
Testing for TB infection among persons or groups who are healthy, have a low risk of exposure and/or have a low risk of progressing to TB disease is discouraged. The positive predictive value of any TB infection diagnostic test for progression to TB disease is low.10 Since the risks of TPT may outweigh the potential benefits of averted TB disease (see Chapter 6: Tuberculosis Preventive Treatment in Adults) in populations at low risk of progression, routine mass screening of entire populations (e.g., all migrants) is discouraged4 except in very specific circumstances (such as during contact investigations or occupational screening programs).
Neither the TST nor IGRA can distinguish between TB infection and TB disease,8 as both tests measure host immune response, which is detectable in both TB infection and TB disease.11 For this reason, when someone being screened for TB infection tests positive with a TST and/or IGRA, further testing is required to rule out TB disease (see Chapter 6: Tuberculosis Preventive Treatment in Adults for further discussion). Due to temporary anergy caused by TB disease, sensitivity of both tests is greatly reduced, and specificity is suboptimal for the diagnosis of TB disease.12 Therefore, neither the TST nor IGRA should be used for diagnosis of TB disease in adults and adolescents (see Chapter 9: Pediatric Tuberculosis for discussion on children ≤12 years). Similarly, serial testing with TST or IGRA during TB disease treatment is not useful to monitor treatment response. Systematic reviews and studies evaluating both qualitative and quantitative changes in TST and IGRA response have shown low reversion rates (positive-to-negative) during and after successful treatment for TB disease.13,14 In addition, reversion of TST and IGRA may occur spontaneously in absence of treatment.15
If testing for TB infection is performed, there must be an a priori commitment to providing TPT or active monitoring should test results be positive. In general, testing for TB infection should consider patient preferences toward treatment and is indicated when there is expected individual benefit from TPT.
We strongly recommend against testing for TB infection in the following situations: (1) in persons who have a low risk of infection and a low risk of progressing to TB disease if infected; (2) to support a TB disease diagnosis in adults and adolescents >12 years of age; (3) for routine mass screening of individuals outside of contact investigations or occupational screening programs; and (4) for the monitoring of TB disease treatment response (good evidence).
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