What is the interferon gamma release assay test (IGRA)?

The Interferon Gamma Release Assay (IGRA) is a blood test used to see whether a person has been infected with Mycobacterium tuberculosis ( the bacteria causing TB). The IGRA test works by measuring the body’s immune response to the TB bacteria.

An IGRA test may be used to diagnose latent TB infection. It is not used to test for active TB disease. A negative IGRA means that you probably don’t have the TB bacteria in your body. A positive IGRA test means that at some point in time you have probably been infected with the TB bacteria. This is called latent TB infection.

What is latent TB infection?

Latent TB infection is when a person has the TB bacteria in their body but the immune system is stopping the infection causing disease. Latent TB infection causes no symptoms and cannot be passed on to other people.

There is a small risk that latent TB infection can progress to TB disease. The risk is increased in young children and old people, as well as people with weak immune systems. TB disease develops if the TB bacteria start to multiply and cause symptoms, such as a fever, unexpected weight loss, tiredness or a cough that won’t go away. Latent TB infection can be treated with special antibiotics to prevent it from progressing to TB disease in the future.

Other tests for latent TB infection

The Tuberculin Skin Test (TST), also known as a Mantoux test, is another test for latent TB infection. It involves a small injection just under the skin, usually on the forearm.

Your nurse or doctor will explain the advantages and disadvantages of the different tests and advise which test is most suitable for your situation. In some situations both TST and IGRA may be required.

Before you have an IGRA test

It is important to let the nurse or doctor know if you:

• have any immune-suppressing illness such as HIV, lymphoma, or kidney disease
• take medication that affects your immune system including steroids (prednisone), cyclosporine or chemotherapy (cancer drugs)
• have had a fever or infection in the past month, such as influenza, measles, or pneumonia
• have received any vaccines in the past month
• have had TB disease in the past, had contact with someone with TB, have received the BCG vaccine, or have travelled or lived overseas.

These conditions may affect the test result.

After you have an IGRA test

You will need to return to your doctor or chest clinic for the test result a few days later. Your nurse or doctor will explain the result and whether any more tests or treatment is required.

Contact your local TB service for more information