TB, also known as tuberculosis, is a very serious, communicable infection that usually infects the lungs, but it can also infect other organs of the body. There are tests that screen for exposure to tuberculosis, as well as diagnostic tests to confirm active TB disease. It is important to talk to your doctor if you think you are at high risk for TB, have been exposed to TB or have symptoms of TB, so the doctor can screen and treat you appropriately.
Tuberculin Skin Test
The Mantoux tuberculin skin test (TST) involves an injection that consists of a small amount of tuberculin purified protein derivative (PPD), according to the Centers for Disease Control and Prevention (CDC). The injection is done on the arm, intradermally. It is necessary for this test to be read within 48 to 72 hours by a trained clinician. The clinician assesses for induration, or swelling, and this is measured in millimeters. The test is interpreted based on the number of millimeters of induration and your risk factors. If the test is positive, it means that you have been exposed to tuberculosis; however, it does not mean that you have progressed to active disease. Your doctor will order a chest x-ray to confirm whether or not you are actively sick if indicated.
Blood Test
There are special blood tests available for testing for TB exposure. As stated by the CDC, these are interferon gamma release assays (IGRA) tests for how the immune system reacts to the TB bacteria. If the person is infected, her white blood cells release interferon gamma because of the TB antigen. Additional tests may be necessary to confirm latent or active TB disease. According to the CDC, when interpreting the result, your doctor should consider your history, as well as any other physical and diagnostic findings.
Chest X Ray
Lesions for TB may appear in the lungs, and they may show up in different ways and different places. A chest x-ray does not confirm a diagnosis; it assists with ruling out the possibility of active pulmonary, or lung, TB.
Sputum Smear and Culture
A sputum smear is done to look for the presence of acid fast bacilli, or AFB. This is a preliminary screening test. A culture of the specimen confirms the diagnosis for Mycobacterium tuberculosis.
