TB skin test
Key points
- The purified protein derivative (PPD) is an antigen used to aid in the diagnosis of Tuberculosis infection.
- The PPD extract is then injected into the most superficial layer under the skin resulting in a blister on the skin.
- Inform your health care provider if you have ever had a positive PPD skin test.
- The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust.
Alternative names
Purified protein derivative standard; PPD skin test; Tuberculin skin test
Definition
The purified protein derivative (PPD) is an antigen used to aid in the diagnosis of Tuberculosis infection. An infection with the bacteria that causes Tuberculosis frequently leads to a sensitivity to these antigens.
How the test is performed
The test site (usually the forearm) is cleansed. The PPD extract is then injected into the most superficial layer under the skin resulting in a blister on the skin.
Because the reaction will take 48-72 hours to develop, you must return to your health care provider within that time for a proper evaluation of the test site. This will determine whether you have had a significant reaction to the PPD test. A reaction is measured in millimeters of induration (hard swelling) at the site.
How to prepare for the test
There is no special preparation for this test. Inform your health care provider if you have ever had a positive PPD skin test. If so, you should not have a repeat PPD test. Notify your health care provider if you are taking certain drugs such as steroids or have a medical condition which can affect your immune system such as cancer. Your PPD may be falsely negative or the cutoffs when interpreting a reaction may be different.
Infants and children:
The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- School age test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
How the test will feel
There will be a brief sting as a needle is inserted just below the skin surface.
Written and revised by
Gerald Hurowitz, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
health.am provides general information, not medical advice. Always consult a qualified health professional about your own health.