Tuberculosis (TB) Blood Test

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KEY POINTS

• The tuberculosis blood test is a screening test that can show if your child has been infected with tuberculosis (TB) bacteria.
• A positive result does not always mean your child has an active TB infection. A negative result usually means that your child does 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 your child has been infected with tuberculosis (TB) bacteria. The test is 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.

Your child should get tested if:

• Your child has been in close contact with someone known or thought to have TB
• Your child has HIV infection or a long-term health condition that weakens the immune system and puts your child at high risk for TB. The immune system is the body’s defense against infection.
• Your child has symptoms of TB such as fever, night sweats, cough, and weight loss
• Your child has 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
• Your child has 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)
• Your child uses illegal drugs
• Your child needs to screened for TB but has had the BCG vaccine. The tuberculin skin test (TST) is not used after a person has been vaccinated, so the blood test is used.

How do I prepare my child 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 child’s arm with a needle. The blood is collected in tubes and sent to a lab.

Ask your child’s healthcare provider how and when you will get your child’s test results.

What does the test result mean?

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

A negative result usually means that your child does 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 child’s 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 your child needs more tests
• What kind of treatment your child might need
• What lifestyle, diet, or other changes your child might need to make

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