The QuantiFERON TB Gold test (QFT-G) is a whole-blood test for use as an aid in diagnosing Mycobacterium tuberculosis infection, including latent tuberculosis infection (LTBI) and tuberculosis (TB) disease. This test was approved by the US Food and Drug Administration (FDA) in 2005. This test is currently NOT available from the South Dakota Department of Health because of the 12 hour processing requirement which makes the testing impractical at the current time.
How does it work?
Blood samples are mixed with antigens (substances that can produce an immune response) and controls. For QFT-G, the antigens include mixtures of synthetic peptides representing two M. tuberculosis proteins, ESAT-6 and CFP-10. After incubation of the blood with antigens for 16-24 hours, the amount of interferon-gamma (IFN-gamma) is measured. If the patient is infected with M. tuberculosis, their white blood cells will release IFN-gamma in response to contact with the TB antigens.
What the advantages?
- Requires a single patient visit to draw blood samples.
- Results can be available within 24 hours.
- Does not boost responses measured by subsequent tests, which can happen with tuberculin skin tests (TST).
- Is not subject to reader bias that can occur with TST.
- Is not affected by prior BCG (bacille Calmette-Guerin) vaccination.
What are the disadvantages and limitations?
- Blood samples must be processed within 12 hours after collection while white blood cells are still viable.
- There are limited data on the use of QFT-G in children younger than 17 years of age, among persons recently exposed to M. tuberculosis and in immunocompromised persons (e.g. impaired immune function caused by HIV infection or AIDS, current treatment with immunosuppressive drugs, selected hematological disorders, specific malignancies, diabetes, silicosis and chronic renal failure).
- Errors in collecting or transporting blood specimens or in running and interpreting the assay can decrease the accuracy of QFT-G.
- Limited data on the use of QFT-G to determine who is at risk for developing TB disease.