Quanti FERON - QuantiFERON-TB Gold

QuantiFERON-TB Gold

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 U.S. Food and Drug Administration (FDA) in 2005.

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 to 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. The QFT-G results are based on the amount of IFN-gamma that is released in response to the antigens.

Clinical evaluation and additional tests (such as a chest radiograph, sputum smear, and culture) are needed to differentiate between a diagnosis of latent TB or active TB.

Advantages of the test are:

• Requires a single patient visit to draw a blood sample.
• 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-Guérin) vaccination.

Disadvantages and limitations of the test are:

• Blood samples must be processed within 12 hours after collection while white blood cells are still viable.
• There is 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 acquired immunodeficiency syndrome, 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.
• False positive results can occur with Mycobacterium szulgai, Mycobacterium kansasii, and Mycobacterium marinum.