The Tuberculin Skin Test is a very simple test to determine if a patient has tuberculosis. The test goes like this: a nurse will take a syringe with a testing material called tuberculin and inject 0.1 cc of solution under the skin on the patient's arm. This solution is absorbed relatively quickly, leaving a small bump about the size of a mosquito bite. For patients who are not infected with TB, this bump will generally dissipate pretty quickly; in my case, a day has gone by and there's no noticable bump there.

For patients who do have tuberculosis, a second bump will appear between 48 and 72 hours after the injection. However, a noticable bump is not always indicative of TB. For instance, patients who have had a vaccine called "BCG" may react positively to the TB test. BCG is not normally administered within the USA.

If a patient reacts positively to the test, a doctor will generally perform more tests to determine if the patient has an active TB infection or not. If not, the doctor will prescribe some preventative medicine, to keep the infection dormant. If the infection is active, treatment will usually begin immediately.

Thanks to Chattering Magpie for informing me that the TB Skin Test is required in the US both before and after travel to foreign countries with a high incidence of TB.
Thanks to BlueDragon for pointing out to me that in the UK, the BCG Vaccine used to be routine at school, and the test is administered first to check for antibodies, which mean that a person is either already immune or infected with TB. The test is done because it is unwise to vaccinate an already immune person, because a huge reaction may occur at the site of injection.

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