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Tuberculosis (TB) - Exams and Tests

Diagnosing active TB in the lungs

Doctors diagnose active tuberculosis (TB) in the lungs (pulmonary TB) by using a medical history and physical exam, and by checking your symptoms (such as an ongoing cough, fatigue, fever, or night sweats). Doctors will also look at the results of a:

Diagnosing latent TB in the lungs

  • A tuberculin skin testtuberculin skin test will show if you have ever had a TB infection. See a picture of a tuberculin skin test camera.gif.
  • Rapid blood tests help detect latent TB.3 They can help diagnose TB when results from a tuberculin skin test are uncertain. These tests also can tell if a person who has had a BCG vaccination has a TB infection. A rapid test requires only one visit to the doctor or clinic, instead of two visits as required for the tuberculin skin test. Rapid blood tests are also called interferon-gamma release assays (IGRAs).

Diagnosing TB outside the lungs

Diagnosing TB in other parts of the body (extrapulmonary TB) requires more testing. Tests include:

  • BiopsyBiopsy. A sample of the affected area is taken out and sent to a lab to look for TB-causing bacteria.
  • Urine cultureUrine culture. This test looks for TB infection in the kidneys (renal TB).
  • Lumbar punctureLumbar puncture. A sample of fluid around the spine is taken to look for a TB infection in the brain (TB meningitis).
  • CT scanCT scan. This test is used to diagnose TB that has spread throughout the body (miliary TB) and to detect lung cavities caused by TB.
  • MRIMRI. This test looks for TB in the brain or the spine.

Testing for HIV infection is often done at the time of TB diagnosis. You may also have a blood test for hepatitis.

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