TST False-Negative Reactions - LabCE.com, Laboratory Continuing Education

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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 referenced as 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 BCG vaccinations
Incorrect TST administration or interpretation