Tuberculosis Skin Testing

Tuberculosis (TB) is a disease usually affecting the lungs (but may involve many other organs) which is caused by the bacterium Mycobacterium tuberculosis. If not treated properly, this disease may be fatal. Two methods of exposure detection exist. The most common is the Mantoux Tuberculin Skin Test also known as a PPD Test. Your skin’s reaction to the injected tuberculin could be a sign that you have had an exposure to TB. The other is a blood test called an IGRA which may be utilized as a confirmatory test for an equivocal skin test or in someone that has been vaccinated for TB in another country.

Test procedure
  • A medical team member will inject 0.1 ml of tuberculin to form a wheal under the skin of the inside of your forearm.
  • The test result is evaluated by an experienced “reader” 48 to 72 hours later.
  • A positive result is any area of induration (hardening and inflammation of the skin) that measures 5mmin diameter or more. A table with additional specifics may be used as a reference for certain at-risk populations.


Who is at risk for testing positive?

Anyone who has been exposed to Tuberculosis through a family member or in the care of a patient may test positive and require further evaluation. Many countries outside the US commonly administer a vaccine for Tuberculosis called BCG. BCG recipients will have a positive skin reaction to the tuberculin injection. IGRA blood tests mentioned above can be useful for testing people with a history of receiving BCG as they will not yield a false positive. In addition, people engaging in high risk behaviors such as IV drug use or those with damaged immune systems are at higher risk for TB.

what if i test positive?

You will be directed to see your medical care provider for confirmatory testing. This typically consists of a chest x-ray to look for signs of the disease, blood testing and sputum culture testing to confirm the presence of the bacterium.

what if these tests confirm that i have tb?

If you are found to have latent TB (you are not sick but have the bacterium in your body) you will be required to be on an antibiotic called INH for up to 9 months. Persons with active TB (you have signs and symptoms of TB along with evidence of the bacterium in your body) will need to be on several medications for up to a year.

For more information on tuberculosis skin testing, see the following websites:

Disclaimer: The links above are to sites independent of The pages will open in a new browser window. The information provided is for educational purposes only, and is not a substitute for professional medical advice, diagnosis, or treatment. If you have or suspect you may have a health problem, you should consult your doctor. Always follow your doctor’s recommendations regarding your specific medical questions, treatments, therapies, and other needs.