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Skin Test

What is tuberculosis?

Tuberculosis (TB) is an infectious disease caused by the tuberculosis germ. TB usually causes disease in the lungs, but may affect other parts of the body.

How is it spread?

TB is only contagious when diagnosed as active disease in the lungs or larynx. It is spread by coughing. Usually, close prolonged contact is required for transmission.

What are the symptoms?

  • Symptoms of TB include fatigue, fever, night sweats, weight loss, coughing, and chest pain. When someone has symptoms from TB, we say the person has “active TB disease”.
  • Tuberculosis is now preventable and curable with proper antibiotic treatment.
  • Only a small percentage of people exposed to the TB germ ever get active TB disease.

Why do I need a tuberculin skin test?

A TB skin test will show whether you have been exposed to TB germs. A TB skin test is done for the following reasons:

  • You are a contact of a person who has infectious TB disease.
  • It is a requirement of employment.
  • To determine past exposure as part of a medical assessment.

What is a TB skin test?

  • TB skin test is a useful tool for diagnosing tuberculosis infection.
  • TB skin test fluid contains PPD (purified protein derivative of killed tubercle bacilli). A tiny amount of this test fluid is injected just under the skin of your forearm. This is not a vaccination. The skin test cannot give you tuberculosis.
  • The test site must be read by a qualified health care practitioner within 48-72 hours to determine if the test is negative or positive. Only reactions of a certain size are considered significant.

What reaction can I expect at the test site?

There may be swelling or redness at the test site and slight discomfort such as itching.

Does a positive skin test mean that I have tuberculosis?

A positive skin test means that you have been exposed to the TB germ at sometime in your life. You have “TB infection”. It does not mean you have tuberculosis disease. You will be referred to your family doctor for assessment. A chest x-ray will be necessary to determine if the TB germs have done any damage to your lungs. Your doctor may prescribe medication to prevent TB.

Additional information

  • Pregnancy or history of previous BCG are not contraindications to receiving this test.
  • Keep a record of your TB skin test. A documented positive skin test is usually not repeated as the test will continue to react positive.


  • Tuberculosis is contagious if active in the lungs or larynx.
  • TB is less common now, but still occurs in Canada.
  • A TB skin test can determine if you have been in contact with TB.
  • Medication is effective in preventing and curing tuberculosis.

For more information call a member of Communicable Disease Services at 519-426-6170, Monday to Friday from 8:30 a.m. to 4:30 p.m.

Adapted from the Region of Peel Public Health Department.

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