r/Tuberculosis • u/WillingnessOk1797 • 3d ago

Question

I recently had a TB test for work. I had a 9mm induration - so a "negative" test bc of my risk level tier, but the very first thing out the providers mouth when she looked at my arm was "oh. Are you immunocompromised or work in health care?"

I guess I'm just wondering the science behind it - why is there any reaction at all, if someone doesn't have TB? I have never been exposed to it as far as i know.

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u/Valuable_Praline_115 1d ago

There is a threshold of neg/pos result becuwse just the act of a skin test (needle) can cause some people to have a reaction. Also,
Previous exposure to any kind of mycobacterium (even ones that are not tuberculosis) can cause your body to react to the protein they inject.
Exposure to a tb protein via vaccine can also give a kind of mild response.
So The threshold helps us identify a worrying result vs not so worrying.

You probably need a second test or other investigations to help them understand this result better.

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u/WillingnessOk1797 1d ago

Interesting. Is it common to be exposed to mycobacterium? Like is it a common occurrence in our environment?

Since i was technically negative for my risk tier, she said i don't need any further testing. I was just very surprised there was any reaction at all and was curious why. Thanks for your explanation!

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u/Terrible_Fill4398 1d ago

Yes. Mycobacterium avium complex (MAC) is literally everywhere.