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Guidance for National Tuberculosis Programmes on the Management of Tuberculosis in Children. 2nd edition. Geneva: World Health Organization; 2014. Guidance for National Tuberculosis Programmes on the Management of Tuberculosis in Children. 2nd edition.Show details
Annex 3Administering, reading and interpreting a tuberculin skin testThis annex gives information on administering, reading and interpreting a tuberculin skin test (TST). A TST is the intradermal injection of a combination of mycobacterial antigens that elicit an immune response (delayed-type hypersensitivity), represented by induration, which can be measured in millimetres. The standard method of identifying people infected with M. tuberculosis is the TST using the Mantoux method. Multiple puncture tests should not be used as these tests are unreliable (because the amount of tuberculin injected intradermally cannot be precisely controlled). This annex describes how to administer, read and interpret a TST using 5 tuberculin units (TU) of tuberculin PPD-S. An alternative to 5 TU of tuberculin PPD-S is 2 TU of tuberculin PPD RT 23. Administration
Figure A3.1Administration of the tuberculin skin test using the Mantoux method. The results should be read between 48 and 72 hours after administration. A patient who does not return within 72 hours will probably need to be rescheduled for another TST.
InterpretationInterpretation of TST depends on two factors: –diameter of the induration; –person's risk of being infected with TB and of progression to disease if infected. Induration of diameter ≥5 mm is considered positive in: –HIV-positive children; –severely malnourished children (with clinical evidence of marasmus or kwashiorkor). Induration of diameter ≥10 mm is considered positive in: –all other children (whether or not they have received BCG vaccination). Causes of false-negative and false-positive TSTs are listed in Table A3.1. Table A3.1Causes of false-negative and false-positive tuberculin skin tests. References1.Guidance for national tuberculosis programmes on the management of tuberculosis in children. Geneva: World Health Organization; 2006. (WHO/HTM/TB/2006.371) [PubMed: 17044200] Copyright © World Health Organization 2014. All rights reserved. Publications of the World Health Organization are available on the WHO website (www.who.int) or can be purchased from WHO Press, World Health Organization, 20 Avenue Appia, 1211 Geneva 27, Switzerland (tel.: +41 22 791 3264; fax: +41 22 791 4857; e-mail: tni.ohw@sredrokoob). Requests for permission to reproduce or translate WHO publications –whether for sale or for non-commercial distribution– should be addressed to WHO Press through the WHO website (www.who.int/about/licensing/copyright_form/en/index.html). Bookshelf ID: NBK214439 What is the induration of a negative TB test?A measurement of 0 mm or a measurement below the defined cut point for each category is considered negative.
What does induration mean for TB test?The skin test reaction should be read between 48 and 72 hours after administration by a health care worker trained to read TST results. A patient who does not return within 72 hours will need to be rescheduled for another skin test. The reaction should be measured in millimeters of the induration (firm swelling).
What is included in a positive skin TB test?A positive TB skin test or TB blood test only tells that a person has been infected with TB bacteria. It does not tell whether the person has latent TB infection (LTBI) or has progressed to TB disease. Other tests, such as a chest x-ray and a sample of sputum, are needed to see whether the person has TB disease.
How many MM is a positive TB test?An induration of 15 mm or more is considered positive in: Always considered positive in any person. Healthy individuals without any risk factors for TB.
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