From the Guidelines
Treating latent tuberculosis (TB) infection does not necessarily lead to a negative QuantiFERON-TB Gold test result. The QuantiFERON test measures immune response to TB antigens and typically remains positive even after successful treatment for latent TB, as it detects memory T-cells that have been sensitized to TB antigens, which persist in the body even after the bacteria are no longer viable 1. Common treatment regimens for latent TB include isoniazid for 6-9 months, rifampin for 4 months, or isoniazid plus rifapentine for 3 months. While these medications effectively eliminate the dormant bacteria, they don't erase the immune system's memory of the infection.
Key Points
- The QuantiFERON test is not recommended for monitoring treatment response or determining if latent TB treatment was successful, as the result can remain positive after treatment 1.
- Completion of the prescribed medication regimen is considered adequate evidence of successful treatment.
- Yearly testing for latent TB (PPD, T-Spot, or QuantiFERON Gold) should be done in patients at high risk, and for patients who are not at high risk, screening should be done at the discretion of the dermatologist 1.
- Caution should be exercised when using the QuantiFERON Gold test, as the result can remain positive after treatment of latent TB 1.
From the Research
Latent TB Treatment and QuantiFERON-TB Gold Test Results
- The QuantiFERON-TB Gold test is used to diagnose latent tuberculosis (TB) infection, but its results after treatment are not always negative 2, 3, 4.
- Studies have shown that after preventive therapy for latent TB, a significant proportion of patients remain QuantiFERON-TB Gold positive 2, 4.
- One study found that 87.5% and 84.6% of patients were still QuantiFERON-TB Gold positive after 3 and 15 months of treatment, respectively 2.
- Another study found that 43% of patients remained QuantiFERON-TB Gold positive after treatment, and that the reversion rate was related to pre-treatment IFN-gamma levels 3.
- A study comparing QuantiFERON-TB Gold Plus and QuantiFERON-TB Gold In-Tube results after preventive therapy found that both tests showed similar trends, but neither was useful for monitoring treatment response 4.
Factors Affecting QuantiFERON-TB Gold Test Results
- Origin from a TB endemic country, recent stay in a TB endemic country, duration of TB exposure, and previous TB disease are independently associated with a positive QuantiFERON-TB Gold test 2.
- IFN-gamma responses were comparable at the start and after 3 and 15 months of treatment, suggesting that the test may not be useful for monitoring treatment response 2.
- Pre-treatment IFN-gamma levels were associated with remaining QuantiFERON-TB Gold positive after treatment 3.
Clinical Implications
- The QuantiFERON-TB Gold test should not be used to monitor the effect of preventive therapy, as most patients remain positive after treatment 2, 4.
- Interferon-gamma release assays, such as QuantiFERON-TB Gold, have a better predictive ability than tuberculin skin tests for detecting latent TB infection and predicting disease progression 5.