TB Skin test is quite simple to go through actually. They will inject Tuberculin into the skin and await how the body reacts, they will need to re-inspect after a couple of days.
If there is clear skin or redness then thats normal. If there is swelling less than 15mm in diameter, then thats acceptable too. Any swelling in the area, thats more than 15mm in diameter is considered as a positive.
A positive for the test, does not impact your immigration medical report. If the skin test comes out as positive, most of the doc offices do an additional chest X-ray and rule out the possibility. For your own precaution, they might put you on a 6 month course of a drug that will remove all traces from your body.
It has been proved that almost 1/3rd of people who get tested for TB skin test, come out as positive. The virus is usually in the body, but the body's defense system keeps winning over it, for life time. When the virus wins, thats when a person contacts the disease. Which is rare, in today's modern medicine world.
This was the information that was relayed to us by our doctor's office.
Wanted to share it with all of you, just in case if you have concerns/questions.
Hope this helps.