The reaction will take 48 - 72 hours to develop. The results of the test depend on the size of the skin reaction and on the person being tested.

A small reaction (5 mm of firm swelling at the site) is considered to be positive in people:

* Who have HIV
* Who are taking steroid therapy
* Who have been in close contact with a person who has active TB

Larger reactions (greater than or equal to 10 mm) are considered positive in:

* People with diabetes or kidney failure
* Health care workers
* Injection drug users

In people with no known risks for TB, a positive reaction means there is 15 mm or more of firm swelling at the site.

Have your doctor interpret the results.