What are the symptoms and how is TB diagnosed?
To test for Mycobacterium tuberculosis infection, a skin test called PPD can be performed in a clinic or doctor’s office. PPD stands for purified protein derivative. It contains pieces of the bacteria and is injected directly under the skin. If someone has been exposed to the bacteria in the past, the immune system will immediately recognize the PPD, resulting in a firm, relatively large bump at the site of the injection. If this reaction occurs, a person is said to have a positive PPD. A positive PPD generally calls for additional testing. An X-ray of the chest is performed to look for signs of active disease. Blood tests, along with sputum (phlegm) samples, may also be sent to a lab for analysis. If the bacteria is found in these samples, it may be tested further to see if it is resistant to any of the drugs commonly used to treat tuberculosis. If someone has a positive PPD but does not have any signs or symptoms of active disease, he or she is said to have latent TB infection. It is
