How Can I Get Tested for TB?
A TB skin test is the only way to find out if you have TB infection. You can get a skin test at the health department or at your doctor's office. You should get tested for TB if
- you have spent time with a person with infectious tuberculosis
- you have HIV infection or another condition that puts you at high risk for tuberculosis disease
- you think you might have tuberculosis disease
- you are from a country where tuberculosis disease is very common (most countries in Latin America and the Caribbean, Africa, and Asia, except for Japan)
- you inject drugs
- you live somewhere in the U.S. where tuberculosis disease is common (most homeless shelters, migrant farm camps, prisons and jails, and some nursing homes)
A health care worker can give you the TB skin test. He or she will inject a small amount of testing fluid (called tuberculin) just under the skin on the lower part of your arm. After 2 or 3 days, the health care worker will measure your reaction to the test. You may have a small bump where the tuberculin was injected. The health care worker will tell you if your reaction to the test is positive or negative. A positive reaction usually means that you have tuberculosis infection.
If you have a positive reaction to the skin test, your doctor or nurse may do other tests to see if you have TB disease. These tests usually include a chest x-ray and a test of the phlegm you cough up. Because the TB bacteria may be found somewhere besides your lungs, your doctor or nurse may check your blood or urine, or do other tests. If you have tuberculosis disease, you will need to take medicine to cure the disease.
If you have recently spent time with someone with infectious TB, your skin test reaction may not be positive yet. You may need a second skin test 10 to 12 weeks after the last time you spent time with the infectious person. This is because it can take several weeks after infection for your immune system to be able to react to the TB skin test. If your reaction to the second test is negative, you probably do not have TB infection.
What if I Have Been Vaccinated with BCG?
BCG is a vaccine for tuberculosis. This vaccine is not widely used in the United States, but it is often given to infants and small children in other countries where TB is common. BCG vaccine does not always protect people from TB.
If you were vaccinated with BCG, you may have a positive reaction to a TB skin test. This reaction may be due to the BCG vaccine itself or to a real TB infection. But your positive reaction probably means that you have TB infection if
- your skin test reaction is large
- you were vaccinated many years ago (because the BCG reaction gets smaller over time)
you have ever spent time with a person with infectious TB - someone in your family has had TB
- you are from a country where TB disease is very common (most countries in Latin America and the Caribbean, Africa, and Asia, except for Japan)
If I Have Tuberculosis Infection, How Can I Keep from Developing Tuberculosis Disease?
Many people who have tuberculosis infection never develop tuberculosis disease. But some people who have TB infection are more likely to develop TB disease than others. These people are at high risk for TB disease. They include
- people with HIV infection
- people in close contact with a person who has infectious tuberculosis
- people who became infected with TB bacteria in the last 2 years
- babies and young children
- people who inject drugs
- people who are sick with other diseases that weaken the immune system
- elderly people
If you have tuberculosis infection (a positive skin test reaction) and you are in one of these high-risk groups, you need to take medicine to keep from developing TB disease. This kind of treatment is called preventive therapy. Also, if you are younger than 35 and you have TB infection, you may benefit from preventive therapy even if you are not in a high-risk group.
People who have tuberculosis infection but do not receive preventive therapy need to know the symptoms of TB. If they develop symptoms of tuberculosis disease later on, they should see a doctor right away.
The medicine usually used for preventive therapy is a drug called isoniazid or INH. INH kills the TB bacteria that are inactive in the body. If you take your medicine as prescribed, preventive therapy will keep you from ever developing tuberculosis disease.
Most people must take INH for at least 6 months. Children and people with HIV infection need to take INH for a longer time.
