Tuberculosis Skin Testing

Tuberculosis, TB, skin testing is common test given to people for screening. For most people, interpreting a skin test for TB is confusing, especially when one is faced with the possibility of having to take medication for a number of months after the results are read. This is to help shed some light on the whole matter.

Although the first priority for tuberculosis control is to treat active TB, the second is certainly to identify and treat those people who are at risk of active disease by discovering what is called latent infection. Latent means that the person is infected but their infection is controlled by their body’s own defense mechanisms. However, latent infections have the potential to develop into active disease at any time, usually under conditions of stress. Finding and treating latent infection can reduce the development of active disease by as much as 90%.
The most common test for the identification of latent TB is the PPD skin test, or the tuberculin skin test( TST). Only those specifically trained should administer the test as there is a specific technique to performing it.

So, who should be tested? High risk people who should be tested include those at high risk who have immunocompromising conditions (conditions that reduce an individual’s body defenses) such as lymphoma, leukemia, chemotherapy, HIV, or on chemotherapy, etc. Other patients, who are considered at moderate risk include those who have diabetes or those on steroid therapy. Patients considered at slightly increased risk are those who are underweight, smoke cigarettes, or have an abnormality on chest x-ray.

Testing implies treatment, so thought needs to be given to who is actually tested. If you are over 65 years old, testing and treatment are indicated only if risk is high( see above). Between the ages of 50-65, the risk of hepatitis from the treatment is about 5%, which is high enough so that testing and treatment are indicated only if the risk of reactivation of latent TB is high or moderate. For those less than 50, the risk of hepatitis is less than 3%( for those less than 35 y/o the risk is less than 1%), testing and treatment is indicated if the risk of reactivation is slightly increased, moderate or high.

So, testing and treatment are not warranted for individuals older than fifty with only a slight increased risk of reactivation and individuals older than sixty-five with moderate or slightly increased risk for reactivation.

As always there is more to be said but this should shine some light on who should be treated and when!

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