FPGEE for National Association of Boards of Pharmacy (NABP) Practice Exam

A tuberculin skin test (TST), or Mantoux test, is used to determine if someone has been exposed to the tuberculosis bacteria. A false-positive reaction occurs when the test indicates that a person has been exposed to tuberculosis when they have not.

Infection with non-tuberculosis mycobacteria can lead to a false-positive reaction because these organisms can stimulate a similar immune response to that of the tuberculosis bacteria, resulting in a positive skin test.

Previous BCG vaccination, which is a vaccine for tuberculosis, can also cause a false-positive result. The vaccine contains live attenuated bacteria (Mycobacterium bovis), and individuals who have received the BCG vaccine may develop a positive reaction on the TST due to the immune response elicited by the vaccine rather than actual infection with tuberculosis.

Recent live-virus vaccination generally does not cause a false-positive reaction in the TST, as the immune response generated by live-virus vaccines (like those for measles, mumps, or rubella) is different and does not interfere with the TST result. Thus, this option does not contribute to false-positive reactions in TST.

When assessing the options, it’s clear that both non-tuberculosis mycobacterial infections and