From the Guidelines
The QuantiFERON-TB Gold test is recommended for detecting tuberculosis infection, especially in individuals 5 years or older who are likely to be infected with Mtb, have a low or intermediate risk of disease progression, and have a history of BCG vaccination or are unlikely to return to have their TST read. This is based on the most recent and highest quality study, which suggests that IGRA is preferred over TST in these cases due to its higher specificity and convenience 1. The test works by measuring the immune system's response to TB bacteria proteins and provides results within 24-48 hours.
Key Points to Consider
- The QuantiFERON-TB Gold test is a blood test that measures the immune system's response to TB bacteria proteins.
- It is more specific for TB detection than the traditional tuberculin skin test (TST) and is not affected by prior BCG vaccination.
- The test is particularly useful for screening high-risk populations, healthcare workers, and individuals with compromised immune systems.
- False negatives can occur in immunocompromised patients, very young children, or those with recent TB exposure, while false positives are rare but possible.
- Additional tests like chest X-rays and sputum cultures are needed for diagnosis of active disease, as a positive result indicates TB infection but cannot distinguish between latent TB infection and active TB disease.
Recommendations for Use
- IGRA is recommended over TST in individuals 5 years or older who meet specific criteria, including those who are likely to be infected with Mtb, have a low or intermediate risk of disease progression, and have a history of BCG vaccination or are unlikely to return to have their TST read 1.
- A TST is an acceptable alternative in situations where an IGRA is not available, too costly, or too burdensome.
- Prior to implementing IGRA testing, each institution and tuberculosis-control program should evaluate the availability, overall cost, and benefits of IGRA for their own setting, as well as consider the characteristics of the population to be tested 1.
From the Research
Interferon-Gamma Release Assays for TB
- The Interferon-Gamma Release Assay (IGRA) is a test used to diagnose latent tuberculosis infection (LTBI) 2, 3, 4.
- IGRA measures the immune response to Mycobacterium tuberculosis antigens, which can indicate the presence of LTBI 3.
- The QuantiFERON-TB Gold In-Tube (QFT-IT) is a type of IGRA that has been used in several studies to diagnose LTBI 2, 4.
Comparison with Tuberculin Skin Test
- The tuberculin skin test (TST) is another test used to diagnose LTBI, but it has some limitations, such as cross-reactivity with Bacillus Calmette-Guérin (BCG) vaccination 3, 5.
- Studies have compared the performance of IGRA and TST in diagnosing LTBI, with some finding that IGRA has better predictive value for progression to active TB 4.
- However, neither IGRA nor TST can accurately differentiate between LTBI and active TB 3, 6, 5.
Clinical Applications
- IGRA has been used in clinical settings to diagnose LTBI and guide treatment decisions 2, 4.
- The test has been shown to be useful in identifying individuals at high risk of progressing to active TB, particularly in high-risk populations such as those with HIV infection 2, 4.
- However, further research is needed to fully understand the clinical applications of IGRA and its role in TB control strategies 6, 5.