The TB skin test is used to find out if someone has been exposed to TB. It involves injecting a small amount of fluid (Tubersol®) under the skin of the formarm. After 48-72 hours, a health care provider will read the skin test and a look for a bump (induration) where the needle was given. A TB skin test is positive if a bump (induration) of a certain size has developed.
What is the cost?
There is no fee for the TB skin test for medical purposes. Proper documentation must be brought from the health care provider who is requesting the test.
Who should have a TB skin test?
- Anyone recently exposed to someone with active TB
- People with a medical condition or who take medication that affects their immune system (e.g. HIV or diabetes)
- Immigrants, refugees or travelers from areas with high rates of TB
- Staff or residents of health care facilities, homeless shelters, or correctional facilities
- people who live or work in Aboriginal communities with high rates of TB
Who should not have a TB skin test?
You should not have a TB skin test if you:
- Have a reliable history of being TB skin test positive in the past.
- Have a history of active TB in the past or history of treatment for inactive or active TB in the past.
- Are allergic to any component of the Tubersol ® or vaccines that have the same components as Tubersol ® which includes phenol.
- Have extensive burns, eczema or other skin lesions where the TB skin test is to be given
- Have had a live virus vaccine (e.g. MMR, shingles, or chickenpox) less than 4 weeks before the TB skin test is to be given. This is because the live vaccines can reduce the immune response to the TB skin test. A TB skin test can be done on the same day as live vaccines.
- Have had a major viral illness (e.g. mononucleosis, mumps, measles) in the past month. Anyone with the common cold in the past month can receive their TB skin test.
What is a one-step TB skin test?
A one-step TB test requires that you come in for the test, and return 48-72 hours later during clinic hours to have it read. If you arrive more than 72 hours later the test cannot be read, as the result is no longer valid.
What is a two-step TB skin test?
The two-step TB skin test involves a first step and reading as described above, and then it is repeated again, at least 1-4 weeks later if the first TB skin test was negative. This step also requires you to return in 48-72 hours to have it read. If either the first or second step is positive, you will need a medical examination and chest x-ray to be sure you are not sick with active TB. For people who may need to have routine TB screening because of their work or other risk factors, only the initial testing should be a two-step. Once a baseline is established, further TB skin testing should only require one-step.
Developed by the Middlesex-London Health Unit and adapted with permission