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Tuberculosis (TB) Blood Test (IGRA)
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What is a TB blood test?
You should have TB blood (or TB skin test) if you:
How can I get a TB blood test?
What if my TB blood is "negative"?
What if my TB blood is "positive"?
What is latent TB infection?
What if I've had the BCG vaccine?
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Tuberculosis (TB) Blood Test (IGRA) (PDF)
What is a TB blood test?
The tuberculosis (TB) blood test, also called an Interferon Gamma Release Assay or IGRA, is a way to find out if you have TB germs in your body. The TB blood test can be done instead of a TB skin test (Mantoux).
There are two kinds of TB blood tests:
- QuantiFERON®-TB
- T-SPOT®.TB
You should have a TB blood (or TB skin test) if you:
- have had frequent close contact with someone who has active TB disease,
- have lived in a country where many people have TB,
- work or live in a nursing home, clinic, hospital, prison, or homeless shelter, or
- have HIV infection or your immune system is not very strong.
Children less than 2 years old should have the TB skin test instead of the TB blood test.
How can I get a TB blood test?
Ask your health care provider. They will draw a small amount of blood and send it to a laboratory. Your health care provider should tell you if your test result is “negative” or “positive” in a few days.
What if my TB blood is “negative”?
A “negative” TB blood test result usually means that you don’t have TB germs in your body.
What if my TB blood is “positive”?
A “positive” TB blood test result means you probably have TB germs in your body. Most people with a positive TB blood test have latent TB infection. To be sure, your doctor will examine you and do a chest x-ray. You may need other tests to see if you have latent TB infection or active TB disease.
What is latent TB infection?
There are two phases of TB. Both phases can be treated with medicine.
When TB germs enter your body, they cause latent TB infection. Without treatment, latent TB infection can become active TB disease.
| Phase 1 – Latent TB Infection | Phase 2 – Active TB Disease |
| TB germs are “asleep” in your body. This phase can last for a very long time – even many years. | TB germs are active and spreading. They are damaging tissue in your body. |
| You don’t look or feel sick. Your chest x-ray is usually normal. | You usually feel sick. Your doctor will do special tests to find where TB is harming your body. |
| You can’t spread TB to other people. | If the TB germs are in your lungs, you can spread TB to other people by coughing, sneezing, talking, or singing. |
| Usually treated by taking one medicine for 9 months. | Treated by taking 3 or 4 TB medicines for at least 6 months. |
What if I’ve had the BCG vaccine?
The BCG vaccine (TB vaccine) may help protect young children from getting very sick with TB. This protection goes away as people get older. People who have had BCG vaccine still can get latent TB infection and active TB disease.
If you had the BCG vaccine and you have a choice of having a TB blood test or a TB skin test, it is better for you to have the TB blood test. This is because the TB blood test is not affected by the BCG vaccine. This means that your TB blood test will be “positive” only if you have TB germs in your body.
Protect your health and the health of your family – get a TB blood test!