Tuberculin skin test

Tuberculosis (TB) is a bacterial infection that can damage the lungs or other parts of the body. The TB skin test can tell if your child has TB bacteria in their body. Many people are exposed to TB and test positive for TB bacteria in their bodies, but they don't get the disease. TB bacteria can stay in your child's body without making your child sick. This is because your child's immune system can keep TB in check.

Your doctor may want your child to have a tuberculin skin test if:

• Your child has been in close contact with someone who has tuberculosis (TB).
• Your child has symptoms that might be causing TB. Symptoms may include a cough that doesn't go away, a fever, or weight loss.

For a tuberculin skin test, you sit down and turn the inner side of your forearm up. The skin where the test is done is cleaned and allowed to dry. A small shot of the tuberculosis antigen (purified protein derivative, or PPD) is put under the top layer of skin. The fluid makes a little bump (wheal) under the skin. A circle may be drawn around the test area with a pen.

In general, there's nothing you have to do before this test, unless your doctor tells you to.

Redness alone at the skin test site usually means you haven't been infected with TB bacteria. A firm red bump may mean you have been infected with TB bacteria at some time. The size of the firm bump (not the red area) is measured 2 to 3 days after the test to find out the result. Your doctor will consider your chance of having TB when looking at the skin test site.

A positive reaction can usually be seen for about 1 week.