The page below is a sample from the LabCE course Tuberculosis Awareness for Health Care Workers. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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TST False Negative Reactions

A false-negative reaction is no induration after a TST, even if the person is infected with Mycobacterium tuberculosis. Some causes of this are:

  • Weakened immune system
  • Recent, old, or overwhelming TB infection
  • Immature immune system (<6 months of age)
  • Some viral illnesses
  • Recent live-virus vaccinations
  • Incorrect TST administration or interpretation