What To Expect From The TB Test

After our previous post: Should You Take A TB Test?, you may be considering getting tested for tuberculosis. The test is pretty straightforward, but if you never had it, it’ll probably be new to you.

In this post, we’ll explore what to expect from the TB test.

nurse with syringeHow it Works

The standard method of testing for tuberculosis is through the Mantoux tuberculin skin test (TST).

Interestingly, “the tuberculin skin test is one of the few investigations dating from the 19th century that are still widely used as an important test for diagnosing tuberculosis.” So it’s been around for a while and seems to still work pretty well.

When you take the test, a nurse will give you a shot on your forearm with 0.1 ml of tuberculin purified protein derfivative (PPD), which tests for TB germs in your body. This fluid is harmless.

After the initial injection, you should notice a wheal (an elevation of the skin, which is pale) form around the spot. So don’t worry about this. It’s just how the test works.

After 2-3 days , you’ll return, and they’ll check the spot of the injection. Note that if you show up after the allotted time, you’ll need to retake the test.


Based on the size of the wheal (and possibly other factors), your test result will be determined positive or negative.

  • If you test negative for TB, you either don’t have the germs in your body or they aren’t showing up.
  • If you test positive for TB, your doctor will work with you to determine the nature of the TB germs. It may be a disease or an infection.
  • Sometimes the test results may not be clear. There can also be false positives and false negatives. So the doctor may want to do additional testing if they find it necessary.

Thankfully, TB can be treated. So if you test positive, it’s good you caught it when you did. You should make sure to follow the doctors treatment plan and instructions for the best outcome.

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