PPD Skin Test
Alternate Names : Purified Protein Derivative Standard, TB Skin Test, Tuberculin Skin Test
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Normal Values
A negative reaction (no induration) or a level of induration below the cutoff for each risk group may indicate lack of infection with the bacteria which causes TB. There are different cutoffs for children, for people with HIV, and other risks groups.
Unfortunately, this is not a perfect test, and up to 20% of people infected with tuberculosis may not have a reaction on the PPD skin test. In addition, individuals with certain conditions which affect the immune system (cancer, recent chemotherapy, late-stage AIDS) may also have a false negative test result.
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