Key points
- A positive test result for tuberculosis (TB) infection means you have TB germs in your body.
- Your health care provider will do other tests to determine if you have inactive TB (also called latent TB infection) or active TB disease.
Why it's important to diagnose TB
Not everyone infected with TB germs becomes sick. As a result, two TB-related conditions exist: inactive TB and active TB disease.
Treatment options are available for both inactive TB and active TB disease.
If you are diagnosed with inactive TB, there are treatments available that can help protect you from getting sick with active TB disease.
People with active TB disease may be able to spread the germs to people they spend time with every day. Without treatment, active TB disease can be fatal.
Protect yourself and others
When to get tested
You may need a TB test if you have:
- Symptoms of TB disease
- Spent time with someone who has active TB disease
- Factors that put you at higher risk for developing active TB disease
- Employment, school, travel, or immigration health screening requirements
How diagnosis works
Anyone with symptoms of TB disease or a positive TB blood test or TB skin test result should be evaluated by a health care provider for TB disease.
Medical evaluation for TB disease
A health care provider may diagnose you with inactive TB or active TB disease based on your:
- Medical history
- Physical examination
- Test for TB infection (TB blood test or TB skin test)
- Chest x-ray
- Laboratory tests to see if TB germs are present (sputum smear and culture)
- Laboratory tests for drug resistance
Medical history
A health care provider will ask you questions about your medical history. For example, the health care provider may ask you if you have:
- Symptoms of TB disease
- Spent time with someone who has active TB disease
- Ever had a positive TB blood test or TB skin test
- Ever been diagnosed with inactive TB or TB disease in the past
- Factors that may increase your risk for becoming infected with TB germs
Physical examination
A physical examination is an essential part of any visit with your health care provider. It can:
- Provide valuable information about your overall health,
- Help with the diagnosis, and
- Reveal other factors that might affect TB treatment.
Testing for TB infection
There are two types of tests for TB infection: the TB blood test and the TB skin test. Ask your health care provider which TB test is best for you.
TB blood test
TB blood tests (also called interferon-gamma release assays or IGRAs) use a blood sample to find out if you are infected with TB germs. The tests measure how your immune system reacts when a small amount of your blood is mixed with TB proteins.
Tell your health care provider if you received a TB vaccine
TB blood tests are the preferred test for people who have received the TB vaccine. Unlike the TB skin test, TB blood tests are not affected by BCG vaccination.
TB skin test
For the TB skin test, a health care provider uses a small needle to put some testing material under the skin. You will need to return to your health care provider in two to three days to see if there is a reaction.
Understanding TB blood test or TB skin test results
A positive test result for TB infection means you have TB germs in your body. Your health care provider will do other tests to determine if you have inactive TB or active TB disease. These tests may include a chest x-ray, and a test of the sputum (phlegm) you cough up.
A negative test result for TB infection means inactive TB or active TB disease is unlikely, but your health care provider may do more tests, especially if:
- You have symptoms of active TB disease, like coughing, chest pain, fever, weight loss, or tiredness.
- You have HIV.
- You were recently exposed to TB germs.
Chest x-ray
Most people with TB disease have TB disease of the lungs. Your health care provider may use a chest x-ray to look for signs of TB disease in your lungs.
Laboratory tests
Your health care provider may collect samples from you. A common sample is a sputum (phlegm) specimen to test for TB of the lungs. To collect the sample, you cough sputum into a small container. Generally, at least three sputum samples are collected and sent to a laboratory for testing. Your health care provider may also collect a urine sample, take tissue samples, or do other tests. These tests can find TB germs that may be outside your lungs.
The laboratory will do tests, such as a smear test and a culture test to see whether there are TB germs in your sample. If the laboratory finds TB germs in your sample, they will also do tests to see which TB medicines can kill the TB germs.
What your diagnosis means
Inactive TB
If you have a positive TB blood test or TB skin test, but your health care provider does not find evidence of TB disease after a medical evaluation, you may be diagnosed with inactive TB.
People with inactive TB are infected with TB germs, but they do not have active TB disease. They do not feel sick, do not have any symptoms, and cannot spread TB to others.
Without treatment, people with inactive TB can develop active TB disease at any time and become sick.
Active TB disease
If you have symptoms of TB disease, a positive TB blood test or TB skin test and your health care provider finds evidence of active TB disease during the medical evaluation, you may be diagnosed with active TB disease.
People with active TB disease feel sick. They may also be able to spread the germs to people they spend time with every day. Without treatment, active TB disease can be fatal.
After a diagnosis
If you are diagnosed with inactive TB or active TB disease, you can be treated. Your health care provider will discuss treatment options with you.
Inactive TB
If you have inactive TB, short and convenient treatments are available that can help protect you from getting sick with active TB disease. You and your health care provider will decide which treatment is best for you.
If you take your medicine as instructed, it can keep you from developing TB disease. Because there are less TB germs, treatment for inactive TB is much easier than treatment for TB disease.
You can prevent active TB disease.
Active TB disease
If you have active TB disease, you will take medicine to treat the disease. You will need to take and finish all of your TB medicine as directed by your health care provider. This is to help you feel better and prevent other people from getting sick.
If you have active TB disease, you will need to take several different TB medicines. This is because there are many TB germs to be killed. Taking several TB medicines will do a better job of killing all the TB germs and prevent them from becoming resistant to the medicines.
Depending on the TB treatment regimen your health care provider prescribes, treatment for TB disease may take four months, six months, or longer.
It is very important that you finish the medicine, taking the drugs exactly as prescribed:
- If you stop taking the drugs too soon, you can become sick again;
- if you do not take the drugs correctly, the TB germs that are still alive may become resistant to those drugs. TB that is resistant to drugs is harder to treat.
Resources
What You Need to Know About Tuberculosis Fact Sheet
Questions and Answers About Tuberculosis Booklet
