Tuberculosis (TB) Blood Test

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KEY POINTS

• The tuberculosis blood test is a screening test that can show if you have been infected with tuberculosis (TB) bacteria.
• A positive result does not always mean you have an active TB infection. A negative result usually means that you do not have TB.
• Talk to your healthcare provider about the results.

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What is a tuberculosis blood test?

The tuberculosis blood test is a screening test that can show if you have been infected with tuberculosis (TB) bacteria. The test is also called an Interferon Gamma Release Assay or IGRA.

Why is this test done?

TB is spread through the air from person to person. It usually causes lung disease, although it can affect almost any part of the body. An active TB infection can be a very serious illness. The TB blood test can find most TB infections before the infection is serious enough to cause any problems. TB infections are no longer common in the US.

You should get tested if you:

• Have been in close contact with someone known or thought to have TB
• Have HIV infection or a long-term health condition that weakens the immune system and puts you at high risk for TB. The immune system is the body’s defense against infection.
• Have symptoms of TB (fever, night sweats, cough, and weight loss)
• Have been in close contact with people where TB is more common, such as a homeless shelter, migrant farm camp, prison or jail, or some nursing homes
• Have traveled to a country where TB is common or has had a lot of contact with a person from such a country (most countries in Latin America and the Caribbean, Africa, Asia, Eastern Europe, and Russia)
• Use illegal drugs
• Have had the BCG vaccine

How do I prepare for this test?

Usually no preparation is needed for this test.

How is the test done?

Having this test will take just a few minutes. A small amount of blood is taken from a vein in your arm with a needle. The blood is collected in tubes and sent to a lab.

Ask your healthcare provider when and how you will get the result of your test.

What does the test result mean?

A positive result does not always mean you have an active TB infection. It may mean that you were exposed and infected with TB in the past, but your body’s immune system is keeping the bacteria under control.

A negative result usually means that you do not have TB.

What if the test result is not normal?

Test results are only one part of a larger picture that takes into account your medical history, physical exam, and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about the result and ask questions such as:

• If you need more tests
• What kind of treatment you might need
• What lifestyle, diet, or other changes you might need to make

If the test is positive, close family members should be tested.