What happens at a TB test's injection site if you don't get the overall TB infection treated?

The injection site would reach a certain size and then go away because it's only reacting to the antigen that was injected into the site, there is not a large enough reaction to maintain over a long period of time. If you have EVER been exposed to TB, you will test positive with the skin test even though the infection is not active and you will be required to have a chest x-ray. Health care professionals determine whether a test is positive or negative based on the size of the bump, called an induration. For example, a healthy individual only tests positive when the induration reaches 15 millimeters (mm) or greater while an individual with a compromised immune system (such as HIV or AIDS) is considered positive with an induration of only 5 mm. In either case, after a few days the bump would disappear, that is why you must have the test read within 48 hours.