What is Interferon Gamma Release Assay (TB-IGRA) Tuberculosis test? 

The IGRA-TB is a screening test that determines if a person has TB infection.

TB is an infectious disease caused by a bacteria called Mycobacterium tuberculosis. The bacteria mostly affects lungs but it may also infect other parts of the body. Most people show active symptoms once they get infected; however, in some people, the TB bacteria may become inactive - the condition is called latent TB. A latent infection can turn active at any time.

A type of white blood cells called T cells play a vital role in the immune response of the body against TB. When our body is exposed to TB bacteria, T cells such as CD4 and CD8 release a compound called interferon-gamma (IFN-γ). IFN-γ then activates the immune system to respond against the bacteria. 

TB-IGRA test detects the presence of IFN- γ specific to CD4 or CD8 cells in the blood. It helps detect both active and latent TB infections. The test is also used to screen for TB infection in a person who has been given a BCG (Bacille Calmette-Guerin) vaccination against TB.

  1. Why is the IGRA TB test performed?
  2. How do you prepare for the IGRA TB test?
  3. How is an IGRA TB test performed?
  4. What do IGRA TB test results mean?

Your healthcare practitioner may order the test if you have been exposed to someone with TB recently or if you have the following symptoms:

TB typically affects the lungs but can spread to other areas, such as the brain, kidneys, spine or joints. The symptoms may vary depending on the area involved. 

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The doctor may also order this test if you:

  • Have HIV or another disease that weakens the immunity
  • Reside or work in a TB-prone area
  • Need to start a medicine that will suppress your immunity 
  • Are an immigrant from a TB-prone area
  • Use illegal drugs

You don’t need special preparation for this test. Let your doctor know if you are taking any prescribed, non-prescribed, illicit or herbal medicines. Medicines that are given to treat cancer may suppress the immunity, thereby affecting test results. The presence of conditions such as HIV/AIDS may affect the test results. 

Your healthcare practitioner will withdraw a small amount of blood from a vein in your arm. The procedure is usually completed in a few minutes. You may experience mild pain or bruising at the site of needle insertion - it will fade away after some time. 

If you have felt dizzy or faint during blood tests in the past, please inform your doctor or nurse so that they can make you feel more comfortable.

Normal results:

A negative result is considered to be normal. This indicates that a person may not have TB infection (active or latent). However, a negative result does not always rule out the possibility of a TB infection.

A false-negative result can be due to the following conditions:

  • Very advanced TB 
  • Conditions that affect the immunity
  • Inflammatory conditions
  • Incorrect handling of the blood sample or faulty testing technique

Abnormal results:

A positive test result is considered to be abnormal and indicates that a person may have TB infection. A false-positive result may be observed if a person is infected with other Mycobacterium species, such as M marinum, M szulgai or M kansasii. False-positive means that the result is positive even though the person is not infected with M tuberculosis.

Your doctor will confirm the diagnosis based on your clinical history, physical examination findings, chest X-ray reports and results of other tests, such as acid-fast bacilli smear and culture tests. (Read more: Acid-fast bacilli staining test)

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.


  1. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; TB Screening (Whole Blood)
  2. Azis L., Jones-López E. C., & Ellner J. J. HIV-associated tuberculosis. Sande’s HIV/AIDS Medicine; 2012. 325–347.
  3. Tau G. and Rothman P. Biologic functions of the IFN-γ receptors. Allergy. 1999 Dec; 54(12): 1233–1251. PMID: 10688427.
  4. Telisinghe L, Amofa-Sekyi M, Maluzi K, et al. [link]. Int J Tuberc Lung Dis. 2017;21(6):690–696. PMID: 28482964.
  5. Lewinsohn DM, Leonard MK, LoBue PA, et al. Official American Thoracic Society/Infectious Diseases Society of America/Centers for Disease Control and Prevention Clinical Practice Guidelines: Diagnosis of Tuberculosis in Adults and Children. Clin Infect Dis. 2017;64(2):111–115. PMID: 28052967.
  6. Moon HW, Gaur RL, Tien SS, Spangler M, Pai M, Banaei N. Evaluation of QuantiFERON-TB Gold-Plus in Health Care Workers in a Low-Incidence Setting. J Clin Microbiol. 2017;55(6):1650–1657. PMID: 28298455.
  7. Centers for Disease Control and Prevention [internet]. Atlanta (GA): US Department of Health and Human Services; Tuberculosis
  8. Los Angeles County Department of Public Health [Internet]. California. US; Tuberculosis (TB) Blood Test (IGRA)
  9. Centers for Disease Control and Prevention [internet]. Atlanta (GA): US Department of Health and Human Services; Deciding When to Treat Latent TB Infection
  10. National Health Service [internet]. UK; Blood Tests

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