Tuberculosis testing

By Jean Cherry, RN, BSN, MBA Apr 13, 2023 • 4 min.

Tuberculosis, also known as TB, is an infectious disease affecting the lungs and potentially the brain, kidney and spine. It is caused by a bacteria called Mycobacterium tuberculosis. When a person with TB coughs, sneezes or speaks, the TB bacteria becomes airborne and can infect those nearby if they breathe in the bacteria. Common symptoms include a cough that lasts over three weeks, coughing up blood and chest pain. TB can be active with symptoms or latent (inactive) in the body for years. If you have latent TB, the risk of it becoming active increases if the body's immune system is weakened from another disease, such as human immunodeficiency virus (HIV).

The number of people diagnosed with TB has been slowly decreasing since 1992. However, the decline of TB cases may be due to underreporting or undetected cases possibly associated with delays in care from the COVID-19 pandemic. In the United States, over 70% of people with TB were born outside of the country. 

People are more likely to get TB from someone they live or work with rather than public areas. Active and latent TB can be cured by treatment with several medications given over a several weeks to months. A person is usually no longer contagious after two to three weeks of treatment. If TB is not treated appropriately, it can be fatal for some people.

How is TB diagnosed?

A skin test, x-ray, sputum or blood test can be used to diagnose TB. Your healthcare provider can help determine which test is right for you.

The Mantoux tuberculin skin test is performed in two visits to a healthcare provider. On the first visit, a small amount of tuberculin is injected underneath the skin of your forearm, making a small raised area. After 48–72 hours, your healthcare provider will check the skin for any palpable, raised, hardened area or swelling at the injection site. If the test is not read within 72 hours, it should be repeated. This is the preferred TB test for children younger than 5 years old.

There are two blood tests available for TB: the QuantiFERON–TB Gold In-Tube test and the T-SPOT TB test. For blood tests, you’ll only need one visit with your healthcare provider. During the visit, your provider will draw blood, and then they’ll send it to a laboratory for analysis. Blood tests are preferred for people who have received the the TB vaccine bacille Calmette–Guérin (BCG) or have trouble making two visits to their healthcare provider.

A negative skin or blood test result means there was no reaction to the test, and it is unlikely that you have active or latent TB. Testing positive for tuberculosis with any of these tests means you have TB, but the tests do not differentiate between the active and latent types of TB. 

Your healthcare provider can order additional tests to determine which type of TB you have. These include chest X-rays or computed tomography (CT) scans to confirm any changes in the lungs from TB. A sputum test can also identify if TB is active when bacteria are present.

Where to get tuberculosis testing

TB Control Offices located in various cities, states and territories, and primary and urgent care clinics in your area may also offer TB testing. You can also contact your local health department, primary healthcare provider, or local hospital about possible locations for TB testing.

Clinically reviewed and updated April 2023.

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