What QuantiFERON-TB Gold Tells You
QuantiFERON-TB Gold is a blood test that detects Mycobacterium tuberculosis infection—both latent tuberculosis infection (LTBI) and active tuberculosis disease—by measuring interferon-gamma release from sensitized T-cells when exposed to TB-specific antigens. 1
How the Test Works
The test measures interferon-gamma (IFN-γ) released by white blood cells in fresh heparinized whole blood when incubated with synthetic peptides representing two M. tuberculosis proteins: 1
- ESAT-6 (early secretory antigenic target-6)
- CFP-10 (culture filtrate protein-10)
These antigens are present in all M. tuberculosis and pathogenic M. bovis strains but are absent from BCG vaccine strains and most nontuberculous mycobacteria (except M. kansasii, M. szulgai, and M. marinum). 1
What a Positive Result Indicates
A positive QuantiFERON-TB Gold result indicates that the person has been infected with M. tuberculosis, but it cannot distinguish between latent infection and active disease. 1, 2 While patients with active TB disease tend to have significantly higher IFN-γ levels than those with LTBI, there is substantial overlap between the two groups, making discrimination difficult. 2
Key Advantages Over Tuberculin Skin Test
The test offers superior specificity compared to TST, particularly in BCG-vaccinated populations, because it is not affected by prior BCG vaccination. 1, 3 Additional advantages include: 1
- Results available within 24 hours without requiring a return visit
- Not subject to reader bias or placement errors inherent to TST
- Does not trigger boosting phenomenon (anamnestic response)
- Less influenced by nontuberculous mycobacterial infections
Clinical Applications
The CDC recommends QuantiFERON-TB Gold may be used in all circumstances where TST is currently used, including: 1
- Contact investigations
- Evaluation of recent immigrants
- Sequential-testing surveillance programs (e.g., healthcare workers)
- One-time screening such as pre-biologic therapy evaluation 3
Important Technical Considerations
Blood must be collected in heparinized tubes and incubated with test antigens within 12 hours of collection to maintain white blood cell viability and ensure accurate results. 4 The test's reproducibility is lower when IFN-γ measurements are near the cutoff point, and automation of the ELISA method reduces variability compared to manual processing. 1, 5
Critical Limitations
The test has important caveats that clinicians must recognize: 1, 6
- Cannot predict who will progress to active TB disease—no prospective data exist linking test results to future TB development
- Sensitivity may be reduced in immunocompromised individuals who have impaired T-cell responses
- Negative results require careful interpretation in high-risk populations
- Errors in specimen collection, transport, or laboratory processing can compromise accuracy