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Tuberculosis (TB) - Exams and Tests
SYMPTOMS & TREATMENTS
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:
- Sputum culture. Testing mucus from the lungs (sputum culture) is the best way to diagnose active TB. But a sputum culture can take 1 to 8 weeks to provide results.
- Sputum cytology.
- Chest X-ray. 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.
- Rapid sputum test. This test can provide results within 24 hours. This test is done only when a person is strongly suspected of having TB.
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 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:
- Biopsy. A sample of the affected area is taken out and sent to a lab to look for TB-causing bacteria.
- Urine culture. This test looks for TB infection in the kidneys (renal TB).
- Cerebrospinal fluid test. A sample of fluid around the spine is taken to look for a TB infection in the brain (TB meningitis).
- CT scan. This test is used to diagnose TB that has spread throughout the body (miliary TB) and to detect lung cavities caused by TB.
- MRI. 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.
Tests during TB treatment
During treatment, a sputum culture is done once a month—or more often—to make sure that the antibiotics are working. You may have a chest X-ray at the end of treatment to use as a comparison in the future.
You may have tests to see if TB medicines are harming other parts of your body. These tests may include:
- Liver function tests.
- Eye tests, especially if you are taking ethambutol for TB treatment.
- Hearing tests, especially if you are taking streptomycin for TB treatment.
Early detection
Public health officials encourage early testing for people who are at risk for getting TB.
© 1995-2011 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated. This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.
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