A TB blood test can find out whether you have the Mycobacterium tuberculosis bacteria in your body. Whether you need to get tested and how often depends on your specific circumstances.

A blood test can check for tuberculosis (TB). If you have a compromised immune system, you may need to have this test periodically, even if you don’t have symptoms.

Other factors can also affect whether you’ll need to get tested for TB, including your risk of coming into contact with the bacteria and your risk of transmitting the infection if you do contract it.

Read on to learn more about TB, who should get a blood test, and what the test involves.

TB is caused by a type of bacteria called Mycobacterium tuberculosis. It most commonly affects the lungs but can also affect other areas of your body.

TB of the lungs spreads through the air. If someone who does not have TB spends time around someone who does, they can inhale the bacteria into their lungs. In 2023, 1.25 million people worldwide died from TB, and it’s the main cause of death for people with HIV.

While TB is contagious, it is not easily spread from one person to another. You would need to be around someone for a long time for the bacteria to spread from them to you.

About one-quarter of the world’s population has the bacteria in their bodies, but it’s inactive in most people. In the United States, TB is relatively uncommon and most cases can be successfully treated.

Symptoms of TB in your lungs include:

  • a bad cough lasting 3 weeks or more
  • chest pain
  • coughing up blood or phlegm from deep in your lungs
  • weakness
  • lack of appetite
  • fever

TB usually affects the lungs but can also infect other parts of your body, such as your lymph nodes, spine, kidneys, or brain.

Having no symptoms does not necessarily mean you don’t have TB. You might have latent (inactive) TB. Without treatment, latent TB can lead to active TB. But latent TB is not contagious.

If you think you may have come into contact with TB bacteria, consult a doctor as soon as possible so they can perform a test if necessary.

Blood tests cannot tell you whether the infection is active or inactive — further tests may be necessary to determine this.

If you have symptoms of TB or may have come into contact with the bacteria, it’s a good idea to consult a doctor so they can assess you and order a test if needed. There are two types of tests for TB: a blood test and a skin test. The blood test is preferred if you’ve received the TB vaccine.

If you have a compromised immune system, you may need to get tested for TB periodically even if you do not have symptoms.

You might also need to get tested if you have a higher risk of TB exposure. This may be the case in the following situations:

  • if you were born in or often travel to a country where TB is common
  • if you live in a large-group setting
  • if you’ve recently been around someone with active TB

If you work in healthcare, your employer might require that you get tested for TB, particularly if you’re likely to come into contact with the bacteria. Some healthcare professionals, such as pulmonologists and respiratory therapists, may be at greater risk.

TB blood tests are also called interferon-gamma release assays (IGRAs). Two tests are currently approved in the United States: QuantiFERON-TB Gold Plus (QFT-Plus) and T-SPOT.TB (T-Spot).

During the TB blood test, a doctor will take a small sample of your blood and mix it with TB proteins. The test will show how much your immune system reacts to the bacteria. It does this by measuring interferon-gamma, a protein that’s produced by a type of immune cell called T cells.

You can also get a skin test to check for the bacteria. Your doctor will determine which test you need, depending on your circumstances.

A positive test result means you have the TB bacteria in your body. You might continue to test positive even after treatment.

A negative blood test result suggests that you’re not likely to have an active or inactive TB infection. But your doctor might want to do more tests if you:

  • have symptoms of active TB
  • have HIV
  • have had recent exposure to TB bacteria

Treatment can depend on whether the infection is latent or active. If you have latent TB, treating it early can reduce the chances that it will become active.

Treatments for latent TB infection include:

  • isoniazid
  • rifapentine
  • rifampin

These antibiotics may be given on their own or as a combination.

If you have treatment-resistant TB or have been in contact with someone who does, you may need to consult a TB expert to determine the best treatment regimen for this circumstance.

TB is caused by a type of bacteria called Mycobacterium tuberculosis. Typical symptoms include a bad cough that lasts 3 weeks or longer, chest pain, and coughing up blood or phlegm from your lungs. Even if they do not have symptoms, healthcare professionals who work in high risk areas and people with compromised immune systems may need to get tested for TB.

A TB blood test shows how your immune system reacts to TB bacteria and can determine whether the bacteria are present in your body. You might continue to test positive even after treatment.

A negative blood test means you are not likely to have a TB infection. But your doctor might want to do more tests to confirm that result, especially if you’ve recently been exposed to the bacteria or if you continue to have symptoms.