Tuberculosis (TB)
Examinations 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 examination, 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 medications 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 an illustration of a tuberculin skin test
.
QuantiFERON-TB Gold is a blood test that has been approved by Health Canada to help detect latent TB. It is faster and more accurate than the skin test, but it is not yet widely available.
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.3
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.
You may have tests to see if TB medications 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
All cases of TB are reported to the local or provincial ministry of health because the disease can spread to others and cause outbreaks. Major health authorities keep track of TB outbreaks and encourage early testing for people who are at risk for developing the disease.
Health Canada and the Canadian Lung Association recommend TB testing for people who:4
- Spend a lot of time with a person who has active TB disease, which can be spread to others.
- Have a human immunodeficiency virus (HIV) infection or another condition that puts them at risk for TB.
- Have had active TB in the past but have not received proper TB treatment.
- Live in Canadian First Nations communities that have a high rate of TB infection.
- Were born in parts of the world where tuberculosis is common, such as Latin America and the Caribbean, Africa, Asia, Eastern Europe, and Russia.
- Live or work in nursing homes, homeless shelters, migrant farm camps, prisons, or jails.
- Are health care workers, especially workers that are likely to be exposed to active cases of TB.
- Have a high-risk medical condition, such as:
- Chronic kidney disease.
- Silicosis, a chronic lung disease caused by inhaling sand-like dust.
- Diabetes.
- Use illegal drugs or abuse alcohol.
- Are travelling to an area where TB is common and have one or more of the risk factors listed above.
People who have a high risk for developing TB usually have a skin test (tuberculin test) on a regular basis. Health professionals often are given a tuberculin skin test when they begin work in a hospital or nursing home, with retesting every 6 to 12 months.
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| Author: | Maria G. Essig, MS, ELS Merrill Hayden | Last Updated: July 25, 2007 |
| Medical Review: | E. Gregory Thompson, MD - Internal Medicine Alfred A. Lardizabal, MD - Pulmonology and Critical Care Medicine/Tuberculosis Andrew Swan, MD, CCFP, FCFP - Family Medicine | |
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