the tb skin test is performed like this
a small amount (less than 1%) of the non-active disease is injected into your arm with a very tiny needle within the skin tissue (not inside your vein) to form a small bubble that eventually shrinks down as the skin absorbs the liquid.
within 48-72 hours-the test will reveal either positive or negative signs. negative is usually a slight red mark that is NOT raised or puffy or no mark left at all. positive is a large,swelled red bump on the arm.
if you have a positive skin test-it does necessarily mean that you have active TB. it means that you have been exposed to it. a chest xray will then be taken that will determine whether or not you have active TB. if active-you are admitted to the hospital for treatment. if non-active, then you are put on medications to help prevent the disease from becoming active in your body and you are monitored closely by your dr
this test is nothing to sweat-i get one every 6 months due to working in a hospital.
The tuberculosis skin test (also known as the tuberculin or PPD test) is a test used to determine if someone has developed an immune response to the bacterium that causes tuberculosis (TB). This response can occur if someone currently has TB or if they were exposed to it in the past. The tuberculin skin test is based on the fact that infection with M. tuberculosis produces a delayed-type hypersensitivity skin reaction to certain components of the bacterium. The components of the organism are contained in extracts of culture filtrates and are the core elements of the classic tuberculin PPD (also known as purified protein derivative). Reaction in the skin to tuberculin PPD begins when specialized immune cells, called T cells, which have been sensitized by prior infection, are recruited by the immune system to the skin site where they release chemical messengers called lymphokines. These lymphokines induce induration (a hard, raised area with clearly defined margins at and around the injection site) through local vasodilation edema, fibrin deposition, and recruitment of other inflammatory cells to the area.
The basis of the reading of the skin test is the presence or absence and the amount of induration (localized swelling). The diameter of the induration should be measured transversely (i.e. perpendicular) to the long axis of the forearm and recorded in millimeters. The area of induration (palpable, raised, hardened area) around the site of injection is the reaction to tuberculin. Again, redness is not measured.
A tuberculin reaction is classified as positive based on the diameter of the induration in conjunction with certain patient-specific risk factors. In a healthy person who is not immunocompromised, induration greater than or equal to 15mm is considered a positive skin test. If blisters are present (vesiculation), the test is also considered positive. In a person with underlying kidney disease, diabetes, or a healthcare worker, 10mm of induration is considered a positive skin test. 5 mm is considered a positive skin test result for patients who are immunocompromised, such as with rheumatoid arthritis patients and Crohn's disease patients. Induration of less than 2mm, without blistering, is considered a negative skin test.
The skin test is checked after 24 hours and then again after 72 hours. This is because for some it takes only 24 hours to illicit an allergic reaction while for others it takes 72 hours. 72 hours is the longest possible time that a person would react with PPD. If after 72 hours, no reaction, then a patient is considered negative of TB based on PPD test although the AFB test (serial sputum collection for 3 days) is the real reliable test for TB.