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Tuberculosis |
          The Mantoux tuberculin skin (TST) test is performed by placing an intradermal injection of 0.1 ml of purified protein derivative (PPD) containing 5 tuberculin units (TU) into the volar surface of the forearm. The injection should be Infection with M. tuberculosis produces a reaction to the tuberculin. The reaction to the TST should be read 48 to 72 hours after the injection by a trained health care worker. Health care workers should not ask patients to read their own skin test results. The skin test is read by palpating the site of injection to find an area of induration. The diameter of the indurated area should be measured across the forearm (perpendicular to the long axis). Erythema (redness) should not be measured. Indurations should be recorded in millimeters, even those classified as negative. If no induration is found, "0 mm" should be recorded. Reading the TST requires training and experience. The skin test is read by palpating the site of injection to find an area of induration. The Skin test interpretation depends on (1) the measurement in millimeters of the induration and (2) the person’s risk of being infected with TB or progression to disease if infected.
A TST reaction of > 5 mm of induration is interpreted as a positive result in the following groups:
A TST reaction of > 10 mm of induration is interpreted as a positive result in persons who do not meet the preceding criteria but who have other risk factors for TB. These include the following:
A TST reaction of > 15 mm of induration is interpreted as a positive result in persons with no known risk factors for TB who except for certain screening programs required by local law or regulation would otherwise not be tested. Targeted skin testing programs should only be conducted among high-risk groups. Guidelines for interpreting tuberculin skin test reactions should also be applied to persons who may have occupational exposure to TB (e.g., health care workers or staff of nursing homes, drug treatment centers, or correctional facilities). Thus, the appropriate cutoff for defining a positive reaction depends on the employee’s individual risk factors for TB, including recent TB exposure and the prevalence of TB in the facility. In facilities where the risk of exposure is very low, So in laymans terms: A tuberculin skin test is done to see if you have ever had tuberculosis (TB) (Mycobacterium tuberculosis). It is done by putting a small amount of TB protein antigens under the top layer of skin on your inner forearm. If you have ever been exposed to the TB bacteria, your skin will react to the antigens by developing a firm red bump at the site within 2 days. The Mantoux skin test uses TB antigens called purified protein derivative (PPD). The test cannot tell if the infection is active or inactive (latent). The Mantoux test uses a measured amount of PPD in a shot that is put under the top layer of skin on your forearm. A Mantoux test is a good test for a TB infection. It is often used when symptoms, screening, or testing, such as a chest X-ray, show that a person may have TB. A tuberculin skin test cannot tell how long you have been infected with TB or if the infection can be passed to others (active TB). With kind permission of CDC (Center for disease control) http://www.cdc.gov/nchstp/tb/ |
Atypical TB
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made with a disposable 27-gauge tuberculin syringe, just beneath the surface of the skin, with the needle bevel facing upward. This should produce a discrete, pale elevation of the skin (a wheal) 6 mm to 10 mm in diameter. Institutional guidelines regarding universal precautions for infection control (e.g., the use of gloves) should be followed.
