Interferon Gamma Release Assay (IGRA) testing for tuberculosis (TB): Questions & Answers (Q&As) for the public

Who are these questions and answers for?

Members of the public.

What is an IGRA test?

This is a blood test that can be used to help in the diagnosis of TB. It may be used in the diagnosis of active tuberculosis disease as well as the diagnosis of dormant (or latent) tuberculosis infection in the absence of active disease.

What is latent TB?

Latent TB is when a person has the bacteria (bugs) that cause TB in their body but they are not causing any disease or symptoms i.e. the bacteria are asleep or dormant. There is a chance that the bacteria may cause disease in the future. 

What is active TB?

Active TB is when the person has symptoms e.g. cough, night sweats, weight loss.

Why do I need an IGRA test?

You may have been in contact with someone who has now been diagnosed with TB, or you may have lived in a country where there are high levels of TB. In some circumstances, the doctors looking after you think that there is a possibility that you have TB and that an IGRA test will help to find out.

I have already had a skin test (a Mantoux or tuberculin skin test). Why do I need another test?

The IGRA test is thought to be a more accurate test than the skin test and will help determine whether you have been infected with TB, and therefore may need treatment.

If the IGRA test is more accurate then why didn't I just have that test done rather than a skin test first?

IGRA tests are new and expensive. The National Institute of Healthcare and Clinical Excellence (NICE) has looked at the accuracy and costs of these tests and recommended a two step approach: a skin test and then, if this is positive, an IGRA test.

What does it involve?

A single specimen of blood.

Who will take the blood for the test?

This depends upon local arrangements. It could be your GP or practice nurse, a TB nurse specialist or a member of the local hospital service.

How long before I get the results?

This varies. It will depend on the reason for which the test was taken, the urgency of the result and how frequently the testing laboratory carries out the test. You should check with your health carer.

When do I have to have the test?

This depends upon how long it was since you were a contact of someone with TB; IGRA testing is usually done at least 6 weeks after the last contact. The exact timing will also depend upon how often the local laboratory runs the test.

What does a positive test result mean?

A positive result means that infection with TB is likely.

What does a negative result mean?

A negative result means that infection with TB is unlikely.

Are there any risks associated with having an IGRA test?

None, apart from the minor discomfort associated with having a blood specimen taken.

Where can I find out more information about IGRA tests?

More information is available in the Q&As for healthcare professionals and in the HPA's position statement.

Where can I find more information about TB in general?

More detailed information can be found on the Health Protection Agency's website.

Last reviewed: 11 January 2012