A TB skin test is one way to detect TB infection. People can get skin tested at the health department or at their doctor’s office. Not everybody is at the same risk for TB infection and, therefore, does not to be tested. However, persons should get tuberculin skin tested if they:
- Are from a country where TB disease is very common (most countries in Latin America and the Caribbean, Africa, and Asia, except for Japan)
- Have spent time with a person with infectious TB
- Inject drugs
- Live somewhere in the U.S. where TB disease is common (most homeless shelters, migrant farm camps, prisons and jails, and some nursing homes).
- They have HIV infection or another condition that puts them at high risk for TB disease
- Think they might have TB disease
If a person has a positive reaction to the skin test, a doctor or nurse may do other tests to see if TB disease is present. These tests usually include a chest x-ray and a test of the phlegm people cough up. Because the TB bacteria may be found somewhere besides the lungs, a doctor or nurse may check the blood or urine, or do other tests. Persons with TB disease need to take medicine to cure the disease.
If a person has recently spent time with someone with infectious TB, the skin test reaction may not be positive yet. The person may need a second skin test 8 to 10 weeks after the last time they spent time with the infectious person. This is because it can take several weeks after infection for one’s immune system to be able to react to the TB skin test. If the reaction to the second test is negative, the person probably does not have a TB infection.
Many people who have TB infection never develop TB disease. In these people, the TB bacteria remain inactive for a lifetime without causing disease. But in other people, especially people who have weak immune systems, the bacteria become active and cause TB disease.