From the Guidelines
A positive QuantiFERON-TB Gold test does not rule out active tuberculosis, as it cannot distinguish between active and latent tuberculosis.
Key Points
- The QuantiFERON-TB Gold test is used to detect Mycobacterium tuberculosis infection, including both latent tuberculosis infection (LTBI) and tuberculosis (TB) disease 1.
- The test detects the release of interferon-gamma (IFN-γ) in fresh heparinized whole blood from sensitized persons when it is incubated with mixtures of synthetic peptides simulating two proteins present in M. tuberculosis: early secretory antigenic target--6 (ESAT-6) and culture filtrate protein--10 (CFP-10) 1.
- A positive result indicates that a person has been infected with M. tuberculosis, but it does not differentiate between latent and active tuberculosis 1.
- To rule out active tuberculosis, additional tests such as a chest radiograph and symptom evaluation are necessary 1.
- The QuantiFERON-TB Gold test is more specific for M. tuberculosis than tests that use tuberculin purified protein derivative (PPD) as the antigen, but it is not perfect and can produce false-positive results 1.
Test Interpretation
- The test result is interpreted based on the amount of IFN-γ released in response to the antigens, with a higher response indicating a greater likelihood of infection 1.
- The FDA-approved interpretation criteria for the QuantiFERON-TB Gold test include a positive result if the TB Response is greater than or equal to 0.35 IU/mL, an indeterminate result if the Nil is greater than 8.0 IU/mL, and a negative result if the TB Response is less than 0.35 IU/mL and the Nil is less than or equal to 8.0 IU/mL 1.
From the Research
Diagnostic Performance of QuantiFERON-TB Gold Test
- The QuantiFERON-TB Gold test is used to diagnose active and latent tuberculosis (TB) infection 2, 3, 4, 5.
- Studies have shown that the test has a high sensitivity for detecting active TB, ranging from 77.8% to 86% 2, 3, 4.
- The test also has a high specificity for identifying subjects who have come into contact with M. tuberculosis 5.
- However, a positive QuantiFERON-TB Gold test does not necessarily rule out active or latent TB, as the test can produce false-negative results 3, 4.
Limitations of the QuantiFERON-TB Gold Test
- The test is not 100% sensitive, and false-negative results can occur, especially in patients with active TB 3, 4.
- The test can also produce indeterminate results, which can make it difficult to interpret the results 2, 3.
- The QuantiFERON-TB Gold Plus test, which is an updated version of the QuantiFERON-TB Gold test, has been shown to have higher sensitivity and fewer false-negative results than the original test 2.
Comparison with Other Diagnostic Tests
- The QuantiFERON-TB Gold test has been compared to other diagnostic tests, such as the tuberculin skin test (TST) and the Standard E TB-Feron ELISA, and has been shown to have similar or better performance characteristics 6, 4, 5.
- The test has been recommended for use in conjunction with clinical and radiological assessments to identify active or latent TB 3.