What could this mean, if a few years ago I had a TB test, tested negative, and then just a few weeks ago, tested positive for TB. I know I am immunized against TB but I find it quite odd that I was tested positive when previously I had tested negative.

  • 2
    1) False positive from your vaccination, 2) you were exposed to TB at some time between your first TB test and your more recent one.
    – Carey Gregory
    Mar 18, 2017 at 16:52

1 Answer 1


You don't specify which test was used to screen for TB, in this answer I will assume that Mantoux test was used.

You probably were vaccinated using Calmette-Guérin vaccine. Unfortunately this has been proven not to give an efficacious immunity against TB infection.

In this scenario there are two chances:

  1. You actually were exposed to M.Tuberculosis.
  2. The Mantoux test is probably a false positive due to your vaccination if you are at low risk for TB infection or to other factors.

Being at low risk means an individual was not:

  • In contact with another person with infectious TB
  • Born or has lived in a high TB prevalence country
  • Continually exposed to populations where TB prevalence is high

In both cases I would personally advise you to contact a doctor to get a chest x-ray and a IGRA quantiferon blood test to further investigate. This is particularly advisable in your case having two different outcomes from serial testing which honestly could increase the possibility of latent TB.

  • Thanks for the answer. I had a chest x-ray done but the doctors indicated it was more likely it was exposure to someone who had TB and not I who had TB>
    – yuritsuki
    Mar 19, 2017 at 18:49
  • You should seek consulence from a specialist who can prescribe a IGRA quantiferon test and if it confirms the diagnosis of latent tuberculosis you should begin treatment for the condition.
    – KingBOB
    Mar 21, 2017 at 20:52

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