A tuberculosis skin test is carried out to know whether you had tuberculosis (TB) previously. It is a relatively simple test and it is carried out by inserting a small amount of antigens (TB proteins) under the upper layer of the skin. Skin on the inner forearm is the preferred place to insert these antigens. If your skin on the inner forearm is normal after 2 days, there is no reason to worry. If you notice a red bump on your inner forearm within two days, it means that your body has been exposed to the TB bacteria previously at some point of time.
This test is carried out to confirm TB when a person exhibits symptoms of this disease or when screening, testing or chest X-ray point towards the presence of TB bacteria.
What is the purpose of this test?
This skin test helps to confirm the presence of TB bacteria in a person due to any of the following reasons:
- Close contact with a TB patient
- Higher risk of exposure to this bacteria (Example: Health care workers)
- Exhibiting TB symptoms like night sweats, weight loss and persistent cough
- Abnormal chest X-ray
- Having an impaired immune system (Example: HIV)
This skin test should not be done on:
- People who have already tested positive for the TB virus
- People who are allergic to TB antigens
- People who have an existing skin rash or disorder
How can you prepare for this test?
Before undergoing a tuberculosis skin test, let your doctor know whether:
- You notice any symptoms of TB
- You had any allergic reaction to TB antigens in the past
- You have come in close contact with a TB patient
- You have lived or worked in a place where TB is prevalent
- You have any immune system impairment such as HIV
Discuss in detail with your doctor about the procedure of the test, risks associated with it or any query that you might have.
