The TB Skin Test (also called Tuberculin, Mantoux or PPD test) is the standard way to determine if someone has the TB germ in his or her body.  Having the germ without being sick is called latent TB infection.  If latent TB infection is not treated, it can become active TB disease.

To perform the test, a very small amount of solution is placed just beneath the surface of your skin to form a very small bubble called a wheal.  A health care worker reads the skin test 48 to 72 hours after it is placed.  Note: after 72 hours (3 days), the test is expired, and unless the result is positive, it cannot be recorded. 

It is normal for the spot where the skin test was placed to be red after the test. This does not mean you have TB.  If there is a hardened area where the skin test was placed, it may mean the skin test is positive.  A nurse will do an assessment to see if it is a positive test.

What about BCG vaccine?  There is a vaccine called BCG (Bacillus of Calmette and Guerin) which is given in parts of the world where there a lot of TB disease.  BCG will not prevent a person from getting latent TB infection, and will not prevent latent TB infection to develop into active TB disease in adults, but it can reduce the severity of active TB disease in children. This is important in countries where there is a great deal of TB because TB has more serious effects in children and can often be lethal.

It is important to know that a BCG vaccination given at birth, does not cause you to have a positive TB skin test as an adult.

People who were vaccinated with BCG should still take the TB skin test.  BCG does not protect people from becoming infected with TB and usually does not change the results of a TB skin test.  Most people who have had BCG vaccine received it when they were children, and BCG usually only causes a positive skin test during the first year after vaccination with BCG.  It is possible for a person to have a positive TB skin test reaction from BCG if they were given BCG vaccine more than once or when they were older, but this is rare.  In the rare cases when someone does get a skin test reaction from BCG, it is usually too small to be considered positive.

For More Information

Tuberculosis Net Teaching Materials:
http://www.tuberculosis.net/

Centers for Disease Control and Prevention TB Guidelines:
http://www.cdc.gov/nchstp/tb/pubs/mmwrhtml/Maj_guide/List_date.htm

Related Programs and Services

Ben Franklin TB Control Program