Quantiferon®-TB Gold (Interferon Gamma Release Assay)
Understanding Quantiferon®-TB Gold (Interferon Gamma Release Assay)
What is Quantiferon®-TB Gold (Interferon Gamma Release Assay)?
The Quantiferon®-TB Gold (Interferon Gamma Release Assay) is a fourth generation assay that helps detect either a latent tuberculosis infection (LTBI) or an active tuberculosis (TB) disease. This test is suggested if you have symptoms of TB, such as persistent cough, fever, and sudden weight loss. It is particularly valuable for individuals who have had recent exposure to TB, healthcare workers, and those with a higher risk of TB infection.
Tuberculosis is an infection that most often affects the lungs and is caused by a bacteria called mycobacterium tuberculosis. An active TB infection is when the affected individual is experiencing TB symptoms. However, latent infection is when the TB organism is present in the individual’s body, but there are no symptoms. People with latent TB infection are not infectious and cannot spread the infection to others. However, if left untreated, this individual may develop an active infection in the future and may be able to transmit the disease.
The Quantiferon®-TB Gold (Interferon Gamma Release Assay) test, also called QuantiFERON-TB Gold Plus (QFT Plus), is a modern alternative to the tuberculin skin test (TST). It assesses the specific immune response to TB, providing a more specific and sensitive analysis than the TST. A Quantiferon®-TB Gold (Interferon Gamma Release Assay) test may be helpful for individuals who have been in close contact with someone with active TB, those with a history of travel to or residence in TB-endemic regions, and individuals with a weakened immune system. It is also used for healthcare workers, as well as in TB screening programs. QFT Plus is an indirect test for M. tuberculosis infection, but is more specific than TST and is unaffected by previous BCG vaccination. It provides doctors with an accurate, reliable and efficient assay for aiding the diagnosis of TB infection.
QFT-Plus is the newest and fourth version of the QuantiFERON TB test. It has new special antigen properties that work better to activate two types of immune cells, called CD4 and CD8 T-cells. This helps the test give a clearer and more complete view of how the body’s immune system is responding.
A positive result is a strong indicator of TB infection. However, a Quantiferon®-TB Gold (Interferon Gamma Release Assay) test cannot be used to distinguish between active and latent TB infection and, therefore, is used in conjunction with risk assessment, radiography, and other medical and diagnostic evaluations.
Usually, no special preparation is required for a Quantiferon®-TB Gold (Interferon Gamma Release Assay) test. The timing of the test can affect the accuracy of the results. If a person is tested too soon after their exposure to tuberculosis bacteria, they may have a false negative result. Doctors recommend testing at least 6 to 8 weeks after the exposure to TB.
Test result ranges are approximate and may differ slightly between labs depending on the methodology and laboratory guidelines. Discuss your test reports with your doctor. Doctors may consider other factors, such as your health history, symptoms, medical conditions, and other test results, to establish a diagnosis of TB disease.
What is Quantiferon®-TB Gold (Interferon Gamma Release Assay) used for?
The Quantiferon®-TB Gold (Interferon Gamma Release Assay) test is done to:
- Detect either active or latent TB tuberculosis in case you have been exposed.
- To screen individuals at higher risk of TB, such as healthcare workers, individuals with recent exposure to TB, and those from regions with a high prevalence of TB.
- To monitor individuals on immunosuppressive therapy since they have a high risk of progression of latent TB infection into active TB.
What does Quantiferon®-TB Gold (Interferon Gamma Release Assay) measure?
The Quantiferon®-TB Gold (Interferon Gamma Release Assay) test measures the immune system’s response to the bacteria that cause tuberculosis (TB). It measures two important types of immune cells T cells—CD4 and CD8 in response to tuberculosis (TB) bacteria. Both these cells play key roles in fighting infections. When a person’s immune system encounters TB bacteria, CD4 T-cells help coordinate and regulate other immune cells, while CD8 T-cells can directly kill infected cells. The test is tailored to activate both CD4 and CD8 T-cells. If these cells recognize the TB proteins, they release a signal called interferon-gamma (IFN-γ); hence the name IGRA (Interferon gamma release assay). By measuring this signal or stimulation from both CD4 and CD8 cells, the test gives a more complete picture of the body’s immune response to TB. This helps doctors better detect both active and latent TB infections, improving the accuracy and reliability of the test.
Interpreting Quantiferon®-TB Gold (Interferon Gamma Release Assay) results
Interpretations
|
NIL TUBE in IU/mL |
ANTIGEN TUBE MINUS NIL TUBE in IU/mL |
FINAL RESULT |
INTERPRETATION |
|
< = 8.00 |
<0.35 > = 0.35 & <25% of Nil tube > = 0.35 & > = 25% of Nil tube |
Negative Negative Positive |
M. tuberculosis infection unlikely M. tuberculosis infection unlikely M. tuberculosis infection likely |
|
>8.00 |
Any result |
Indeterminate |
This may be due to excessive levels of circulating gamma interferon or the presence of heterophile antibodies. |
Answers to Patient Concerns & Frequently Asked Questions (FAQs) about Quantiferon®-TB Gold (Interferon Gamma Release Assay)
Frequently Asked Questions about Quantiferon®-TB Gold (Interferon Gamma Release Assay)
Q. What is the Quantiferon®-TB Gold (Interferon Gamma Release Assay) test?
Q. When should one get the Quantiferon TB Gold Plus test?
Q. What happens if the Quantiferon®-TB Gold (Interferon Gamma Release Assay) test result is positive?
Q. What happens if TB is not treated timely?
Q. How does tuberculosis spread?
Q. What is Latent TB infection?
Q. Can tuberculosis be cured?
Book a Quantiferon®-TB Gold (Interferon Gamma Release Assay) test at home near me
References
- Babu K, Philips M, Subbakrishna DK. Perspectives of Quantiferon TB Gold test among Indian practitioners: a survey. J Ophthalmic Inflamm Infect. 2013 Jan 11;3(1):9. [Accessed 26 Oct. 2023]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3605069/
- Franken WP, Timmermans JF, Prins C, Slootman EJ, Dreverman J, Bruins H, van Dissel JT, Arend SM. Comparison of Mantoux and QuantiFERON TB Gold tests for diagnosis of latent tuberculosis infection in Army personnel. Clin Vaccine Immunol. 2007 Apr;14(4):477-80. [Accessed 26 Oct. 2023]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1865601/ this Page
- Adigun R, Singh R. Tuberculosis. [Updated 2023 Jul 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441916/
- Tuberculosis [Internet]. WHO; 21 Apr. 2023 [Accessed 26 Oct. 2023]. Available from: https://www.who.int/news-room/fact-sheets/detail/tuberculosis#:~:text=Overview,Tuberculosis%20is%20preventable%20and%20curable.
- Basic TB Facts [Internet]. CDC; 20 Mar. 2016 [Accessed 26 Oct. 2023]. Available from: https://www.cdc.gov/tb/topic/basics/default.htm
- Narasimhan P, Wood J, Macintyre CR, Mathai D. Risk factors for tuberculosis. Pulm Med. 2013;2013:828939. [Accessed 26 Oct. 2023]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3583136/#:~:text=However%20at%20the%20population%20level,accelerate%20progression%20to%20TB%20disease.
- TB Screening (Whole Blood) [Internet]. Rochester, NY: University of Rochester Medical Center; [Accessed 26 Oct. 2023]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=tb_screen_blood
Other tests
