What is Tuberculosis?

Tuberculosis (TB) is a serious disease caused by a germ (bacteria) that spreads through the air when a person with untreated TB disease of the lungs coughs, sneezes, sings or talks.

TB usually affects the lungs but can also affect other parts of the body like glands, bones, joints, kidneys, the brain and reproductive organs.

TB is curable. In British Columbia, medicines to prevent or cure TB are free through Provincial TB Services and public health units. For more information on TB, visit HealthLinkBC File #51a Tuberculosis (TB).

What is a TB skin test?

You can use a TB Skin Test (TST) to look 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 bacteria before. This test alone cannot tell whether the bacteria are sleeping or awake.

A TST does not tell you if you have TB disease. If you have symptoms of TB disease, visit your health care provider. Symptoms of TB disease in 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.

Who should get a TB skin test?

You may need a TST for various reasons, including screening for work, school or volunteering. You also may need a TST if you were in contact with someone who had untreated TB disease of the lungs, or you have certain health conditions or medications that weaken your immune system.

TB infection happens when the TB germs are sleeping (dormant) in your body. If you have TB infection, you can talk with your health care provider about the best ways to prevent 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 the 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.

First appointment

A health care 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

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 cannot go to school, work or volunteering, but you may need more tests to make sure you do not have 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, visit HealthLinkBC File #51b Sputum testing for tuberculosis (TB).

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. If this reaction occurs, 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?

People with:

• Prior allergic response or severe reaction (for example, 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 TB disease or TB infection

If you cannot get a TST, 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 ImmunizeBC at https://immunizebc.ca/finder to search for your local health unit’s contact information.

For more information

For more information, including information about BC Centre for Disease Control (BCCDC) TB clinics, visit www.bccdc.ca/health-info/diseases-conditions/tuberculosis