Role of Interferon-Gamma Release Assay (IGRA) in TB Diagnosis and Treatment
Introduction to IGRAs
- The Centers for Disease Control and Prevention (CDC) recommends that IGRAs are valuable diagnostic tools for detecting Mycobacterium tuberculosis infection, but cannot distinguish between latent TB infection (LTBI) and active TB disease, and should not be used alone for diagnosing active TB 1, 2
Primary Uses of IGRAs
- IGRAs are used for the detection of M. tuberculosis infection (latent TB) 1, 2
- IGRAs cannot distinguish between latent TB infection and active TB disease 2, 6
Advantages of IGRAs over TST
- The CDC recommends IGRAs for persons with a history of BCG vaccination due to higher specificity 4, 8
- IGRAs have higher test completion rates in populations with historically low rates of return for TST reading, such as homeless persons or drug users 4
Limitations of IGRAs
- Negative IGRA results do not exclude TB infection, especially in immunocompromised individuals 1, 2
- Indeterminate or borderline IGRA results may require repeat testing 9, 10
Recommended Testing Approaches
- The CDC recommends using IGRAs for TB contacts, with follow-up testing 8-10 weeks after exposure if the initial test is negative 3, 4
- For occupational screening of healthcare workers, either TST or IGRA can be used without preference 3, 4
Interpretation of IGRA Results
- A positive IGRA in symptomatic patients or those at high risk for TB progression should be considered evidence of M. tuberculosis infection 1, 2
- In healthy persons with low likelihood of TB infection, a single positive IGRA should not be taken as reliable evidence of infection (may be false positive) 1, 2