Interferon gamma release assay test (IGRA test)

The interferon gamma release assay (IGRA) test is a blood test used to see whether a person has tuberculosis (TB) infection.

TB infection (also known as latent TB infection or 'sleeping' TB) is when you have TB germs in your body, but they are not making you sick. Your body's immune system is stopping the germs causing any damage. There are no symptoms with TB infection and the germs cannot be passed to other people.

TB infection is different from TB disease which is when TB germs wake up or increase in number and make you sick and able to pass the germs on to other people. If the IGRA blood test shows you have TB infection, your doctor can prescribe medicine to stop TB disease.

More information about TB infection can be found here: TB infection

Last updated: 21 January 2025

How is the IGRA performed?

An IGRA is a blood test that needs 4 small tubes of blood. You can eat and drink as normal before the test. It works by measuring the body's immune response to the germs that cause TB.

Before you have an IGRA test

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

have any immune weaking illnesses such as HIV, cancer, or kidney disease
take medicine that affects your immune system such as steroids (e.g. prednisone), or chemotherapy (cancer drugs)
have had a fever (>38°C) or infection in the past month, such as the flu, measles, or a chest infection
have had any vaccines in the past month
have had TB in the past or contact with someone with TB.

After you have an IGRA test

If your IGRA result is positive, you may have come into contact with TB germs in the past. A negative IGRA result means it’s unlikely you have been in contact with TB germs. Your nurse or doctor will explain the result and whether you need any more tests or treatment.