Tuberculosis (TB) Skin Test
What is TB?
Tuberculosis (TB) is a serious disease caused by germs (bacteria) that spread through the air. A person with active TB disease in their lungs can spread TB disease to another person. When a person with active TB coughs, sneezes, sings or talks, they spread TB germs through the air.
TB usually affects the lungs, but can also affect other parts of the body like glands, bones, joints, kidneys, the brain and reproductive organs.
You can cure TB. In B.C., medicines to prevent or cure TB are free through Provincial TB Services and public health units. For more information on TB, see: HealthLinkBC File #51a Tuberculosis (TB).
What is a TB Skin Test?
You can use a TB Skin Test (TST) to test for TB infection. You can do a TST to see if you have ever been exposed to TB. It tells your health care provider if your body has “seen” the TB bacteria before. A TST cannot tell how long you have been infected with TB. This test alone does not tell whether the TB bacteria are latent (dormant or sleeping) or active.
Who should get a TB Skin Test (TST)?
Visit your health care provider for a check-up if you have symptoms of TB disease, have been in contact with someone with active TB disease or want to know if you have latent TB infection.
Symptoms of active TB disease of the lungs include a cough for 2 to 3 weeks or longer, bloody spit, fever, night sweats, loss of appetite, unexplained weight loss, tiredness, chest pain and shortness of breath.
Latent TB infection (LTBI) happens when the TB germs are sleeping (dormant) in your body. If you have LTBI, you can talk with your healthcare provider about the best ways to prevent active TB disease. The TB germ may remain sleeping in your body your entire life or it can wake up, start multiplying (growing) and make you sick with active TB disease. There is no way to know if or when this will happen. The chance of this happening increases when a person’s immune system is weakened. This is because the immune system is what keeps the TB germs in a sleeping state and prevents them from multiplying.
How is a TB Skin Test done?
A TST is a two-part test.
A healthcare practitioner uses a tiny needle to inject a small amount of a test substance called Tubersol® under the top layer of skin on your forearm.
Second appointment 48 to 72 hours later
You must go back to the clinic 48 to 72 hours later to have a health care practitioner read your test. People with TB infections usually respond with a raised, firm reaction at the site where the Tubersol® was injected.
Your health care provider will check the area where the skin test was given for a reaction. They will measure the induration (swelling under the skin) and tell you your test results.
What do TB Skin Test results mean?
A negative TST usually means that you do not have TB germs in your body. Most people do not need further testing.
A positive TST means you may have TB germs in your body.
- A positive TST result does not mean you can’t go to school, work or volunteering, but you may need more tests to make sure you don’t have active TB disease
- A positive TST means you do not need to have another TST in the future. Keep a record of your positive TST results as proof
The TST results, your reason for testing and your general health may mean further TB testing such as a TB blood test, chest X-ray or sputum samples.
A chest X-ray is a picture of your lungs that your health care provider examines to see if TB bacteria are growing in your lungs.
The sputum (mucous or phlegm deep in your lungs produced from coughing) is sent to a laboratory and tested to see if there are TB bacteria present. For more information, see HealthLinkBC File #51b Sputum Collection for Tuberculosis (TB) Testing.
What are the possible reactions after a TB Skin test?
You can expect some redness at the skin test site. The site may itch, but it is important that you do not scratch it, since this may cause redness or swelling that could make it hard to read the skin test. If itching is a problem, put a cold, wet face-cloth on the site. Do not cover the site with a bandage.
A strong reaction may cause mild pain or redness that can last for several weeks. Talk to your health care provider if you have a fever, swelling in your arm or swollen lymph nodes in your armpit.
It is important to stay in the clinic for 15 minutes after getting your TST because there is an extremely rare possibility, less than 1 in a million, of a life-threatening allergic reaction called anaphylaxis. Anaphylaxis has been very rarely reported following a TST with Tubersol®. These reactions can occur in people without a history of a TST. This may include hives, difficulty breathing or swelling of the throat, tongue or lips. Should this reaction occur, your health care provider is prepared to treat it. Emergency treatment includes administration of epinephrine (adrenaline) and transfer by ambulance to the nearest emergency department. If symptoms develop after you leave the clinic, call 9-1-1 or the local emergency number.
It is important to always report serious or unexpected reactions to your health care provider.
Who should not get a TB Skin Test?
- Prior allergic response or severe reaction (e.g. blistering) to a TST or any allergy to the components of Tubersol®
- Documentation of a previously positive TST result
- Previous Interferon Gamma Release Assay (IGRAs) reactive (TB blood test)
- Previous active TB disease or LTBI
If you should not get a TST, then your health care provider will ask you questions about your health and decide if you need other TB tests instead.
Where can I get a TB Skin Test?
Depending on your reason for getting a TST, you may get it for free or you may have to pay if it is for school, work or volunteering. Service locations vary throughout the province. TSTs may be available at your public health unit, travel health clinic, pharmacy or doctor’s office.
Contact your local health unit to find out where you can get a TST in your area. Visit the ImmunizeBC Health Unit finder to find your local health unit’s contact information at https://immunizebc.ca/finder.
You may also find TB skin testing locations on the HealthLinkBC FIND Services and Resources Directory: www.healthlinkbc.ca/services-and-resources/find-services.
For more information
For more information about TB, including information about BC Centre for Disease Control (BCCDC) TB clinics, visit: www.bccdc.ca/health-info/diseases-conditions/tuberculosis.