Tuberculosis (TB) is caused by a highly infectious bacteria called Mycobacterium tuberculosis. Though it is most commonly associated with the lungs, TB can also affect the brain, kidney, liver and other areas of the body. It is a rather stealthy disease, with symptoms that aren't always apparent until the disease is in its advanced stage. The bacteria are transmitted by respiratory droplets when the infected person sneezes, coughs, laughs or even sings. Anyone exposed to persons with the disease should be tested for TB.
Mantoux Skin Test
The Mantoux skin test, also called PPD, is performed by injecting a small amount of a purified protein derivative under the skin in the forearm. About 48 to 72 hours after the injection, the health care provider will obtain results of the test by measuring the red and swollen area at the site of injection. Positive results do not confirm a TB diagnosis, but merely demonstrate exposure to the bacteria. In cases of a positive test, the results will always be positive for future tests. It takes about six weeks after initial infection for PPD to return a positive result.
Chest X-Ray
If a Mantoux skin test shows positive results, the doctor will follow up by obtaining a chest X-ray. The U.S. Centers for Disease Control and Prevention (CDC) states that 85 percent of people with tuberculosis have it in their lungs. Therefore a chest X-ray diagnosis is useful in determining a state of active disease. If infected, the X-ray will look abnormal because of accumulation of fluid in the lungs or pocket-like cavities encasing the bacteria. Positive results do not confirm a diagnosis of TB but is strongly suggestive of the disease.
Sputum Cultures
Also known as AFB smear and culture, this diagnostic test, along with positive skin test and X-ray results, is the final step in definitively diagnosing an active infection of tuberculosis. A sputum specimen is obtained for identifying Mycobacterium tuberculosis and to determine whether TB is confined to the lungs or has spread to other body parts. This diagnostic tool is also used to determine the most appropriate drug with which to treat the disease and will likewise be used to monitor the effectiveness of treatment.
