There are two tests for tuberculosis (TB) infection: the TB blood test and the TB skin test. A positive result means you have TB germs in your body; further tests then show whether it is inactive TB (latent TB infection) or active TB disease. Testing and treatment protect you, your family and friends, and your community.
Why get tested
You may need a TB test if you have:
- symptoms of TB disease;
- spent time with someone who has active TB disease;
- risk factors for developing active disease;
- a job, school, travel or immigration screening requirement.
You may need a test even if you feel fine: TB germs can live in the body for years without causing illness — inactive TB — and people with inactive TB can't spread it.
Who should be tested
Higher risk of exposure — if you:
- were born in, or often travel to, countries where TB is common, including some in Asia, Africa and Latin America;
- live or lived in large group settings such as homeless shelters, prisons or jails;
- recently spent time with someone with active TB disease;
- work where TB spreads more easily — hospitals, shelters, correctional facilities, nursing homes.
Higher risk of developing TB disease once infected — some people with inactive TB never get sick; others do months or years later, when their immune system can no longer hold the germs back. The risk is higher if you:
- have a weaker immune system from certain medicines or conditions such as diabetes, cancer or HIV;
- were infected in the last two years;
- are a baby or young child, especially under five;
- inject illegal drugs;
- have other diseases that weaken the immune system;
- are elderly;
- were not treated correctly for TB before.
People at low risk generally don't need TB tests.
The two tests
| TB blood test | TB skin test | |
|---|---|---|
| Also called | interferon-gamma release assay (IGRA) | — |
| How it works | a blood sample is mixed with TB proteins to see how your immune system reacts | a provider puts testing material under the skin with a small needle |
| Visits | one | a return visit in 2–3 days to check for a reaction |
| After the BCG vaccine | preferred — not affected by BCG | can be affected |
Many people born outside the United States have had the TB vaccine, Bacille Calmette-Guérin (BCG) — tell your provider if you have. Ask which test is best for you. More: blood test, skin test.
Where to get tested
At the health department or your health care provider's office; state or local TB programs can help. Public and private health plans may cover the cost.
Results
- Positive: you have TB germs. Further tests — often a chest X-ray and a sputum (phlegm) test — show whether it's inactive TB or active disease.
- Negative: TB is unlikely, but your provider may test further if you have symptoms (such as coughing, chest pain, fever, weight loss or tiredness), have HIV, or were recently exposed.
Keep a written record of a positive result: you may test positive again in future, even after treatment, and the record will help.
Sources
Based on "Testing for Tuberculosis," Centers for Disease Control and Prevention; a work of the United States government in the public domain. The source's stock photograph is not reproduced.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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