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Tuberculin Skin Test (TST)

  • This reaction is quantified by measuring the diameter of skin induration (thickening not reddening) at the site of the injection.
  • Various conditions can suppress this reaction.
  • The reaction only shows that the person has at some time been infected with M. tuberculosis.
  • There is a sliding cut point based on risk of progression to TB disease. People who are more likely to progress to active disease have lower cut point than those less likely to progress to active disease.
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