Is there a need to repeat the Quantiferon (Interferon-Gamma Release Assay) test?

From the Guidelines

Repeating the Quantiferon test is generally not necessary unless specific circumstances warrant it, such as recent contact with someone with infectious TB, a new TB exposure, or initiation of immunosuppressive therapy. The Quantiferon test is designed to detect Mycobacterium tuberculosis infection with a single administration, and results are typically definitive [ 1 ]. However, retesting may be appropriate in certain situations:

• If the initial test was indeterminate or borderline
• If there's been a new TB exposure since the first test
• If a patient has started immunosuppressive therapy that might affect test results
• As part of regular screening for healthcare workers or others with ongoing TB exposure risk If retesting is needed, it should generally be performed at least 8-12 weeks after any potential exposure to allow sufficient time for the immune response to develop [ 1 ]. The test works by measuring the immune system's response to TB antigens, specifically the release of interferon-gamma from T-cells that have previously been sensitized to TB. This biological mechanism remains stable over time in most individuals, which is why routine repeat testing is unnecessary unless clinical circumstances change. Additionally, guidelines for HIV-infected patients recommend repeat testing in those with advanced HIV disease who initially had negative results but subsequently experienced an increase in CD4 cell count [ 1 ].

In terms of specific recommendations, for persons with recent contact with persons who have infectious TB, negative QFT-G results should be confirmed with a repeat test performed 8--10 weeks after the end of exposure [ 1 ]. This approach ensures that the test results are accurate and reliable, and it helps to prevent the spread of TB.

Key considerations for repeating the Quantiferon test include:

• The timing of the test: at least 8-12 weeks after any potential exposure
• The patient's clinical circumstances: recent contact with someone with infectious TB, new TB exposure, or initiation of immunosuppressive therapy
• The patient's immune status: those with advanced HIV disease who initially had negative results but subsequently experienced an increase in CD4 cell count By taking these factors into account, healthcare providers can make informed decisions about when to repeat the Quantiferon test and ensure that patients receive appropriate care and treatment.

From the Research

Need to Repeat Quantiferon Test

• The decision to repeat the Quantiferon test depends on various factors, including the initial test results and the individual's clinical context 2, 3, 4.
• If the initial test result is indeterminate, repeating the test may be necessary to obtain a determinate result 2.
• However, studies have shown that indeterminate results are more common in elderly and immunocompromised patients, and repeating the test may not always yield a determinate result 2.
• In cases where the initial test result is positive, repeating the test may not be necessary, as the risk of developing active tuberculosis is low 5.
• The QuantiFERON-TB Gold In-tube assay has been shown to be a useful diagnostic tool for latent tuberculosis infection, but its utility in monitoring the effect of preventive therapy is limited 3.
• Serial QuantiFERON testing can be used to measure the acquisition of Mycobacterium tuberculosis infection, but the interpretation of results is confounded by immunological and technical variability 4.
• A study found that a significant proportion of individuals with a history of positive tuberculin skin test results had negative results on subsequent tests, including the QuantiFERON test 6.

Factors Influencing Test Results

• Elderly and immunocompromised patients are more likely to have indeterminate results 2.
• Lymphocytopaenia and hypoalbuminaemia are significantly associated with indeterminate laboratory findings 2.
• Recent immigration from TB endemic countries and long duration of exposure are risk factors for a positive QuantiFERON test result 3.
• Technical assay variability can contribute to uncertain conversions in serial testing 4.

Clinical Implications

• The QuantiFERON test should be interpreted with caution in elderly and immunocompromised patients 2.
• Repeating the test may not always be necessary, and clinical context should be taken into account when making decisions about repeat testing 2, 5, 3.
• The test should not be used to monitor the effect of preventive therapy, as most patients remain QuantiFERON positive after therapy 3.