From the Guidelines
QuantiFERON levels measure the immune response to TB bacteria by detecting interferon-gamma released by white blood cells when exposed to TB antigens, with a positive result indicating likely TB infection and a negative result suggesting no infection. The QuantiFERON test is a blood test used to detect tuberculosis (TB) infection, and it is particularly useful for people who have received the BCG vaccine, as it doesn't cause false positives like the traditional TB skin test might 1. The test doesn't distinguish between latent TB infection and active TB disease, so additional testing like chest X-rays or sputum cultures may be needed for diagnosis. Some of the key aspects of QuantiFERON testing include:
- Performance of the test in young children, especially those aged <5 years, and in persons with impaired immune systems, including those with HIV/AIDS 1
- Determination of the subsequent incidence of TB disease after latent TB infection has been either diagnosed or excluded with QuantiFERON 1
- Changes in QuantiFERON results during therapy for both latent TB infection and TB disease 1 If you've had a QuantiFERON test, your healthcare provider should interpret the results in the context of your symptoms, medical history, and risk factors for TB exposure 1. It's also important to note that the QuantiFERON-TB Gold test, the QuantiFERON-TB Gold In-tube test, and the T-SPOT TB test are approved by the FDA as aids for detecting TB infection 1. In terms of guidelines, all HIV-infected patients should be tested for M. tuberculosis infection by TST upon initiation of care, and annual testing should be considered for those who have negative results by TST but are at ongoing risk for exposure to tuberculosis 1.
From the Research
QuantiFERON Test Overview
- The QuantiFERON test is an indirect immunoassay based on blood, used for the diagnosis of tuberculosis (TB) infection 2.
- It measures the release of interferon-gamma (IFN-γ) from peripheral blood lymphocytes in response to TB-specific antigens 3, 4.
Interpretation of QuantiFERON Results
- The results of the QuantiFERON test are interpreted based on the level of IFN-γ released, with higher levels indicating a positive result 5.
- A threshold of 0.35 IU/mL is commonly used to determine a positive result, but this may vary depending on the specific test and population being studied 4, 5.
- In some studies, a higher threshold of 4 IU/mL has been used to maximize both sensitivity and specificity for the diagnosis of tubercular uveitis 5.
Factors Influencing QuantiFERON Results
- The results of the QuantiFERON test can be influenced by various factors, including immunosuppression, age, and ethnicity 2, 4.
- In immunosuppressed individuals, the test may produce false-negative results due to decreased IFN-γ production 4.
- The test may also be less sensitive in individuals with low lymphocyte counts, such as those with HIV/AIDS or undergoing immunosuppressive therapy 4.
Clinical Applications of QuantiFERON
- The QuantiFERON test is used for the diagnosis of latent and active TB infection, as well as for monitoring treatment response 3, 6.
- It has been shown to be useful in identifying individuals with latent TB infection who are at risk of progressing to active disease 5.
- The test has also been used to monitor the response to anti-TB treatment, although its utility in this setting is still being evaluated 6.