TB Testing and Diagnosis

TB Testing and Diagnosis

There are two types of tests used to detect latent TB infection: the TB skin test and the IGRA blood test.  A positive test result indicates that a person is infected with TB bacteria. It does not tell whether a person has a latent TB infection or has TB disease. Other tests, such as a chest x-ray, must be used to determine if a person has TB disease.

Who should be tested?

Certain people have a higher risk of TB infection and should be tested for TB. People should be tested for TB if they:

  • Are from a country where TB disease is common, including Latin America, the Caribbean, Africa, Asia, Eastern Europe, and Russia
  • Have had close contact over time with a person who has active TB disease
  • Live or work in a high-risk setting such as long-term care facilities, homeless shelters, or correctional facilities
  • Work with patients who have an increased risk for TB

TB tests are usually not needed for people who have a low risk of infection.

Testing for a Tuberculosis infection

There are two types of tests for TB infections: a skin test and a blood test. A health care provider will decide which test is appropriate. If either a blood test or a skin test is positive, a health care provider will determine if the patient has a latent TB infection or TB disease.

Skin Test

The TB skin test is performed by injecting a small amount of fluid, known as tuberculin, into the skin.

A health care provider will examine the injection site within 48 to 72 hours to determine if it is a positive result.

Additional tests are needed to distinguish between a latent TB infection and TB disease.

Blood Test

A health care provider will draw a patient’s blood and send it to a laboratory for analysis.

If the result is positive, this means that the person is infected with TB. It does not distinguish between a latent TB infection and TB disease.

Diagnosing latent TB infection and TB disease

A health care provider should evaluate anyone who has TB symptoms or a positive TB test result by for TB disease. If a person has a negative TB test result, but still has symptoms, they should still be evaluated for TB.

Diagnosing Latent TB Infection

A person is diagnosed with a latent TB infection if they have a positive TB test but a medical evaluation does not indicate TB disease. A health care provider will decide whether to treat a latent TB infection based on an individual’s risk factors.

Diagnosing TB Disease
  • TB is diagnosed through many tests including a physical examination, medical history, and a chest x-ray. If someone is diagnosed with TB, their health care provider will recommend multiple medications.
  • TB disease should be suspected in people with any symptoms of TB, including loss of appetite, night sweats, fever, and fatigue.
  • Symptoms of a TB infection in the lungs (pulmonary TB) include chest pain, coughing for longer than three weeks, and coughing up blood. Symptoms of TB in other parts of the body will depend upon what area is affected.