Reasons, Preparation and Procedure For Conducting Tuberculin Skin Tests

Submitted on March 27, 2012

Tuberculin skin tests are typically recommended when trying to determine whether the patient has ever contracted tuberculosis (that is, TB).

Why Tuberculin Skin Test is done

Tuberculin skin testing is recommended when trying to figure out if the individual has been exposed to TB. This is a TB infection that is suspected due to indicators like symptoms of tuberculosis. For instance, a test like a chest X-ray might reveal the possibility of TB and this test is used to confirm the TB diagnosis. However, further details are not possible with this particular test. For instance, the results do not reveal for how long the TB has been present. The test also does not indicate whether the TB present is active or whether it is presently latent (inactive). As a result, a tuberculin skin test cannot be used to determine whether the TB can spread to others. Some people who should go in for this tuberculin skin test include those in health care who might have some TB exposure and those who, due to any reason, might have had close contact with a patient suffering from tuberculosis. There are circumstances wherein, despite needing this test, it might not be recommended such as in cases of skin rash where the results of this test might be obscured because of it.


Preparation for this skin test involves letting your doctor know about a long list of things such as whether the TB vaccination has ever been administered and if you have HIV.


Tuberculin skin tests involve a little of TB protein (that is, antigens) being placed just under your body’s top skin layer, typically on the inner forearm. Purified protein derivative (PPD) is the term given to these TB proteins. A white bump results but this is small and under the skin. You will have a follow up visit after this skin test in about 2 days or so, to examine the area. Due to these antigens, if at any point of time you have had exposure to the bacteria which causes this infection (known as Mycobacterium tuberculosis) you will experience a reaction. This is because the antigens force the skin to react. This is not an alarming reaction but merely a red bump which develops in that area (inner forearm) in about 2 days. It is a carefully small measured amount of PPD that you will receive in the shot. Positive tuberculin skin tests mean that there has already been exposure to TB.