Questions and Answers About TB
Testing and Treatment
Should I get tested for TB?
You should get tested for TB if
- You have spent time with a person known or suspected to have TB disease; or
- You have HIV infection or another condition that weakens your immune system and puts you at high risk for TB disease; or
- You have symptoms of TB disease; or
- You are from a country where TB disease is very common (most countries in Latin America and the Caribbean, Africa, Asia, Eastern Europe, and Russia); or
- You live somewhere in the United States where TB disease is more common such as a homeless shelter, migrant farm camp, prison or jail, and some nursing homes; or
- You inject illegal drugs.
What are the tests for TB infection?
The TB skin test
The TB skin test may be used to find out if you are infected with TB bacteria. You can get a skin test at the health department or at your doctor’s office. A health care worker will inject a small amount of testing fluid (called tuberculin or PPD) into the skin on the lower part of your arm. After 2 or 3 days, you must return to have your skin test read by the health care worker. You may have swelling where the tuberculin was injected. The health care worker will measure this swelling and tell you if your reaction to the test is positive or negative. A positive reaction usually means that you have been infected by someone with TB disease.
If you have recently been infected with TB bacteria, your TB skin test reaction may not be positive yet. You may need a second skin test 8 to 10 weeks after the last time you spent time with the person with TB disease. This is because it can take several weeks after infection for your immune system to react to the TB skin test. If your reaction to the second test is negative, you probably do not have TB infection.
TB blood tests
TB blood tests use a blood sample to find out if you are infected with TB bacteria. The tests measure the response of TB proteins when they are mixed with a small amount of blood. If your health department does offer the TB blood tests, only one visit is required to draw blood for the test. Examples of these TB blood tests include QuantiFERON®-TB Gold in-Tube test (QFT-GIT) and T-Spot® .TB test.
What if I have a positive test for TB infection?
If you have a positive reaction to the TB skin test or TB blood test, your doctor or nurse may do other tests to see if you have TB disease. These tests usually include a chest x-ray. They may also include a test of the sputum you cough up. Because the TB bacteria may be found somewhere other than your lungs, your doctor or nurse may check your urine, take tissue samples, or do other tests. If you have TB disease, you will need to take medicine to treat the disease.
What if I have been vaccinated with BCG?
BCG is a vaccine for TB. 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 getting TB.
If you were vaccinated with BCG, you may have a positive reaction to a TB skin test. This reaction may be due to infection with the TB bacteria. However, in some people, BCG may cause a positive skin test when they are not infected with TB bacteria.
A positive reaction is more likely to mean you have been infected with TB bacteria if:
- You recently spent time with a person who has TB disease; or
- You are from an area of the world where TB disease is very common (such as most countries in Latin America and the Caribbean, Africa, Asia, Eastern Europe, and Russia); or
- You spend time where TB disease is common (homeless shelters, migrant farm camps, drug-treatment centers, health care clinics, jails, prisons).
Unlike the TB skin test, TB blood tests are not affected by prior BCG vaccination. The TB blood tests are less likely to give a false-positive result in people who have received BCG.
If I have latent TB infection, how can I keep from developing TB disease?
Many people who have latent TB infection never develop TB disease. But some people who have latent TB infection are more likely to develop TB disease than others. Those at high risk for TB disease include:
- People with HIV infection
- People who became infected with TB bacteria in the last 2 years
- Babies and young children
- People who inject illegal drugs
- People who are sick with other diseases that weaken the immune system
- Elderly people
- People who were not treated correctly for TB in the past
If you have latent TB infection (a positive TB skin test reaction or positive TB blood test) and you are in one of these high-risk groups, you need to take medicine to keep from developing TB disease. This is called treatment for latent TB infection. There are several treatment options.
One treatment option for latent TB infection is isoniazid (INH). Taken for 6 to 9 months, INH kills the TB bacteria that are in the body. If you take your medicine as instructed by your doctor or nurse, it can keep you from developing TB disease. Children, adolescents, and people infected with HIV who have latent TB infection need to take INH for 9 months. The preferred regimen for children 2-11 years old is 9 months of daily INH.
Another effective treatment option for people with latent TB infection is the 12-dose regimen. This regimen of INH and rifapentine (RPT) is taken once a week for 3 months under directly observed therapy (DOT). This means the patient will meet with a health worker at a place they both agree on, and the health worker will observe the patient taking the medicine.
You and your health care provider must decide which treatment option is best for you.
Because there are less bacteria, treatment for latent TB infection is much easier than treatment for TB disease. A person with TB disease has a large amount of TB bacteria in the body. Several drugs are needed to treat TB disease.
Sometimes people are given treatment for latent TB infection even if their TB skin test reaction or TB blood test result is negative. This is often done with infants, children, and people infected with HIV who have recently spent time with someone with TB disease. This is because they are at very high risk of developing TB disease soon after they become infected with TB bacteria.
If you start taking treatment for latent TB infection, you will need to see your doctor or nurse on a regular schedule. It is important that you take all the pills as prescribed. The doctor or nurse will check on how you are doing. Some people have serious side effects from these medicines. If you have any of the following side effects, call your doctor or nurse right away:
- No appetite
- Yellowish skin or eyes
- Fever for 3 or more days
- Abdominal pain
- Tingling in the fingers and toes
- Pain in lower chest or heartburn
- Feeling itchy
- Skin rash
- Easy bruising
- Bleeding from gums
- Nose bleeding
- Urine becomes dark or brown in color
- Aching joints
Warning: Frequent or heavy drinking of alcoholic beverages (wine, beer, and liquor) while taking treatment for latent TB infection can be dangerous. Check with your doctor or nurse for more information..
People who have latent TB infection need to know the symptoms of TB disease. If they develop symptoms of TB disease, they should see a doctor right away.
What if I have HIV infection?
Because HIV infection weakens the immune system, people with latent TB infection and HIV infection are at very high risk of developing TB disease. All persons with HIV infection should be tested to find out if they have latent TB infection. If they have latent TB infection, they need treatment as soon as possible to prevent them from developing TB disease. If they have TB disease, they must take medicine to treat the disease.
TB disease can be prevented and treated, even in people with HIV infection.
If I was exposed to someone with TB disease, can I give TB to others?
If you were exposed to someone with TB disease, you may become infected with TB bacteria, but you would not be able to spread the bacteria to others right away. Only persons with TB disease can spread TB to others. Before you would be able to spread TB bacteria to others, you would have to breathe in TB bacteria and become infected. Then the bacteria would have to multiply in your body and cause TB disease. At this point, you could possibly spread TB bacteria to others.
Some people develop TB disease soon (within weeks) after becoming infected, before their immune system can fight the TB bacteria. Other people may get sick years later, when their immune system becomes weak for another reason. Many people with TB infection never develop TB disease.
In most people who breathe in TB bacteria and become infected, the body is able to fight the bacteria to stop them from growing. The bacteria become inactive, but they remain alive in the body and can become active later. This is called latent TB infection. People with latent TB infection cannot spread TB bacteria to others. People who have latent TB infection can be treated to prevent developing TB disease.
- Page last reviewed: December 21, 2012
- Page last updated: September 18, 2014
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