Patient education: Tuberculosis screening tests (The Basics)

What is tuberculosis? — Tuberculosis, or "TB," is an infection that usually affects the lungs.

The germ that causes TB can travel in the tiny drops of fluid that spray when a person coughs or sneezes. If you are exposed to the germ by breathing in these drops, you can get infected.

Doctors use the term "TB infection" to mean that the germ is in your body but is not making you sick. Sometimes, it can cause symptoms later, even months or years after getting infected. When this happens, it is called "TB disease."

What is TB screening? — Screening is a way to check for an infection or disease when a person does not have any symptoms. It is possible to have TB infection without knowing it.

Who should be screened for TB? — Doctors recommend screening for people who are at increased risk of getting TB.

For example, your doctor might want you to get screened if you are at risk for new infection. This might be the case if you:

●Were exposed to someone with TB

●Live or work in a homeless shelter or correctional facility

●Use injection drugs

●Have spent a long time in a part of the world where TB is common

●Work in health care and might be around people with TB

They might also want to screen you if you have certain conditions that affect your immune system, like HIV infection or cancer.

What tests are used to screen for TB? — There are 2 ways to screen for TB:

●Skin test – This is called a "tuberculin skin test," or "TST."

●Blood test – This is called an "interferon-gamma release assay," or "IGRA."

Your doctor can recommend which test to get based on your situation.

How do I prepare for a TB test?

●For the skin test, you do not need to do anything special to prepare.

●For the blood test, you need to get a "blood draw." Your doctor or nurse will tell you where to go for this. It might help to wear a short-sleeve shirt to your appointment.

What happens during a TB skin test? — For the skin test:

●Your doctor or nurse will clean the skin on your lower arm.

●They will give you a shot of fluid in your lower arm. The fluid contains tiny pieces of the dead TB germ.

●Two or 3 days later, you will see your doctor or nurse again. They will look at the spot where you got the shot. They will check to see if there is a bump, and measure how big the bump is (figure 1). Based on the size of the bump and your situation, the doctor or nurse can tell if your test is positive or negative.

If you get a bump on your skin, it will go away on its own in a few days.

What happens during a TB blood test? — For a blood draw, a needle is used to take a small amount of blood from your arm (figure 2). Collecting the blood only takes a few minutes. The blood is then tested in a lab.

Tell the person who takes your blood:

●If you take "blood thinner" medicines or if you have a bleeding problem – They will make sure that your bleeding is under control before you leave.

●If you have a latex allergy – Some of the supplies used for blood draws might contain latex.

●If you have a preferred arm to use

Most of the time, getting blood taken does not cause problems. You might have a little soreness or bruising where the needle went in.

What do my results mean? — Your doctor or nurse will tell you when to expect your results, and will contact you with the results. Or if you use an online "patient portal," you might get an alert there when your results are ready.

The results of a skin or blood test can be:

●Positive – This means that you most likely have been infected with TB. Your doctor will need to do more tests to confirm the result. That's because it is possible to get a "false-positive" result. This is when the test comes back positive even though you do not actually have TB.

●Negative – This means that you most likely have not been infected with TB. In some cases, a person can still be infected and get a negative test. This is called a "false-negative" result. Depending on your situation, your doctor might repeat the test in a few months.

If your test was positive, your doctor or nurse will do more tests to figure out if you have TB infection or TB disease. This is important because the treatment plans are different.

More on this topic

Patient education: Tuberculosis (The Basics)

Patient education: Tuberculosis (Beyond the Basics)