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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:
- Sputum cultures. Testing mucus from the lungs (sputum culture) is the best way to diagnose active TB. If TB bacteria grows from your samples, sensitivity testing is done on the bacteria. These tests will show which medicines will kill the bacteria. Results of sensitivity tests can take between 1 and 6 weeks because TB-causing bacteria grow very slowly. Your doctor may start treatment before results are returned if it's likely that you have TB. Researchers are working on new tests that may give quicker results.
-
Chest X-rays. A chest X-ray cannot
diagnose active TB. A chest X-ray usually is done if you have:
- A positive tuberculin skin test (also called a TB skin test, PPD test, or Mantoux test).
- Symptoms of active TB, such as a persistent cough, fatigue, fever, or night sweats.
- An uncertain reaction to the tuberculin skin test because of a weakened immune system, or to a previous bacille Calmette-Guerin (BCG) vaccination.
Diagnosing latent TB in the lungs
A
tuberculin skin test will show if you have ever had a
TB infection. See a picture of a
tuberculin skin test
.
Rapid blood tests have been approved by the U.S. Food and Drug Administration (FDA) to 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.
Diagnosing TB outside the lungs
Diagnosing TB in other parts of the body (extrapulmonary TB) requires more testing. You may have:
- A sample of the affected area taken out (biopsy). The sample is sent to a lab to look for TB-causing bacteria.
- A urine culture to look for TB infection in the kidneys (renal TB).
- A sample of fluid around the spine (cerebrospinal fluid) taken to look for a TB infection in the brain (TB meningitis).
- A CT scan to diagnose TB that has spread throughout the body (miliary TB) and to detect lung cavities caused by TB.
- An MRI scan to look 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.4
Tests during TB treatment
During treatment, sputum tests are done once a month-or more often-to make sure the antibiotics are working. You may have a chest X-ray at the end of treatment to use as a comparison in the future.
WebMD Medical Reference from Healthwise
Tuberculosis (TB) Topics
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