PPD skin test
Alternate Names : Purified protein derivative standard, TB skin test, Tuberculin skin test, Mantoux test
Normal Values
A negative reaction (no induration) or a size of hard swelling that falls below the cutoff for each risk group may mean that you have not been infected with the bacteria that cause TB. There are different cutoffs for children, people with HIV, and other risk groups. Unfortunately, this is not a perfect test. Up to 20% of people infected with the bacteria that cause TB may not have a reaction on the PPD skin test. In addition, certain conditions that affect the immune system (cancer, recent chemotherapy, late-stage AIDS) may cause a false-negative test result.
What do Abnormal Results Mean?
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.
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