Tuberculosis (TB): Diagnosis
To diagnose tuberculosis (TB), your healthcare provider will gather five important pieces of information during the complete history and physical examination:
History of Exposure
Getting an accurate history is important in diagnosing and treating TB. Like any disease, early intervention and treatment is very important.
Tuberculin Skin Test
The tuberculin skin test (or PPD) uses an extract of killed TB germs. The killed germs are injected into the skin. If a person has been infected with TB, a lump will form at the site of the injection. This is a positive test. This often means that TB germs have infected the body. It does not often mean the person has active disease. People with positive skin tests but without active disease cannot transmit the infection to others.
Previous vaccination for TB compromises the validity of the tuberculin skin test. Newer blood tests, have helped identify those with true TB infection.
Tuberculosis Blood Test
There are two new blood tests that have recently been developed to test for exposure to tuberculosis germs. They are still used in research settings but some hospitals and clinics are using them in place of the tuberculin skin test.
Chest X-ray
If a person has been infected with TB, but active disease has not developed, the chest X-ray will often be normal. Most people with a positive PPD (skin test) or TB blood test have normal chest X-rays and continue to be healthy. For such people, preventive medication may be recommended.
However, if the germ has attacked and caused inflammation in the lungs, an abnormal shadow may be visible on the chest X-rays. For these people, diagnostic tests (sputum tests) and treatment often are appropriate.
Sputum Test
Samples of sputum coughed up from the lungs can be tested to see if TB germs are present. The sputum is examined under a microscope (a "sputum smear") to look for evidence of the TB organisms. The organisms are then grown in the lab to identify them as TB germs and to determine what medications are effective in treating them. These studies are referred to as culture and susceptibility testing. State health department labs and reference labs can perform such testing.
This information has been approved by Gwen Huit, MD (April 2009).
