Tuberculin skin test

You will be asked to have a tuberculin skin test to see if you have potentially been exposed to the TB bacteria. This could be if your doctor suspects you may have the disease and require treatment, or if you are at risk of catching it and need protection. 

You may be more at risk of getting TB if you:

• are in close contact with a person with active TB disease
• were born in a country with higher rates of TB
• traveled to or lived for more than one month in a country with higher rates of TB
• have a weakened immune system such as being HIV-positive
• live or work in certain institutional settings, eg, healthcare facilities.

Read more about TB.

The tuberculin skin test involves having a small amount of liquid, called tuberculin, injected into the very top layer of the skin on your forearm. This is done with a small needle and syringe. The test, which is done by specially trained laboratory technicians, does not contain live bacteria and cannot cause TB.

• You may get a small blister at the injection site, but this usually disappears within the first 30 minutes.
• Sometimes the site may bleed a little and the nurse may cover it with a cotton wool swab. This can be removed after 10 minutes and discarded. 
• Do not apply creams or band-aids to the injection site and avoid scratching it. To relieve an itchy reaction, apply ice or something cold. 

Image credit: Bruce Blausen Wikimedia Commons

After 2 to 3 days of having the tuberculin skin test, the laboratory technician will measure your skin’s reaction to the tuberculin. If more than 3 days have passed before you get the site checked, the assessment will not be reliable and you will need another skin test.

Interpretation of the test result depends on a number of factors, including whether you are known to have been in contact with somebody who has TB, whether you have previously had a BCG vaccine, your age and your medical history.

If your tuberculin test is negative, you may be advised to either:

• have a repeat test in 1–2 weeks
• have a BCG vaccination
• have no further follow-up.

If your injection site shows a reaction, you may be advised to either:

• have treatment for latent TB
• have further tests for TB disease
• avoid further tuberculin tests
• consult with your usual doctor
• have no further follow-up.