Latent TB Infection: Selecting a Test to Detect TB Infection

Latent TB Infection: Guide for Diagnosis and Treatment

Diagnosis

Selecting a Test to Detect TB Infection

• IGRAs are the preferred method of testing for:
  • Groups of people who have poor rates of return for TST reading and interpretation (e.g., homeless persons)
  • Persons who have received BCG vaccination
• TST is the preferred method for testing for:
  • Children under the age of 5 years
• Either TST or IGRA may be used without preference for other groups that are tested for LTBI.

Key Points

• Routine testing with both TST and IGRAs is NOT recommended; however, there are certain situations where results from both tests may be useful.

Certain Situations Where Results from both TST and IGRA May Be Useful

Routine testing with both TST and IGRA is not recommended.  However, results from both tests might be useful in the following situations:

• When the initial test is negative and:
  • The risk for infection, progression to disease, and/or a poor outcome is high (e.g., HIV-infected persons or children under 5 years of age who are exposed to a person with infectious TB).
  • There is clinical suspicion for TB disease (e.g., signs, symptoms, and/or radiographic evidence suggestive of TB disease) and confirmation of M. tuberculosis infection is desired.
  • Taking a positive result from a second test as evidence of infection increases detection sensitivity.
• When the initial test is positive and:
  • Additional evidence of infection is required to encourage acceptance and adherence to treatment (e.g., foreign-born health care workers who believe their positive TST is due to BCG).
  • The person has a low risk of both infection and progression from infection to TB disease. Requiring a positive result from the second test as evidence of infection increases the likelihood that the test reflects infection. An alternative is to assume, without additional testing, that the initial result is a false positive or that the risk for disease does not warrant additional evaluation or treatment, regardless of test results.

In addition, repeating an IGRA or performing a TST might be useful when the initial IGRA result is indeterminate, borderline, or invalid and a reason for testing persists.

Multiple negative results from any combination of these tests cannot exclude M. tuberculosis infection. Steps should be taken to minimize unnecessary and misleading testing of persons at low risk. Selection of the most suitable test or combination of tests for detection of M. tuberculosis infection should be based on the reasons and the context for testing, test availability, and overall cost of testing.