TB Tests

By: Mary Anna Stone

What is a TB Test?


  • Tuberculin skin test: The TB skin test is performed by injecting a small amount of fluid (called tuberculin) into the skin in the lower part of the arm.
  • A person given the tuberculin skin test must return within 48 to 72 hours to have a trained health care worker look for a reaction on the arm. The health care worker will look for a raised, hard area or swelling, and if present, measure its size using a ruler. Redness by itself is not considered part of the reaction.
  • The skin test result depends on the size of the raised, hard area or swelling. It also depends on the person’s risk of being infected with TB bacteria and the progression to TB disease if infected.

How to know if you have Tuberculosis

  • Positive skin test: This means the person’s body was infected with TB bacteria. Additional tests are needed to determine if the person has latent TB infection or TB disease. A health care worker will then provide treatment as needed.
  • Negative skin test: This means the person’s body did not react to the test, and that latent TB infection or TB disease is not likely.

Why should I get a TB test?

You want to get one becuase, 1. You want to see if you have tuberculosis and 2. If you want to work in the medical field they make you get a TB test.

What causes TB?

In simplest terms, if the TB germ is present in your lungs, you have TB. But that doesn't necessarily mean you'll feel sick. If your immune system is doing its job, the germ should not cause much trouble. You might experience some coughing after the initial infection, but you probably won't have any symptoms. Most importantly, you won't be able to infect anyone else. This is called latent TB.
Tuberculosis (TB) Test