Background
About the TB skin test
The TB skin test is a test used to determine if a person is infected with TB bacteria. In this test, a standardized solution made with purified protein derivative (PPD), which is derived from tuberculin, is injected under the skin.
Typically, PPD produces a T-cell mediated delayed-type hypersensitivity reaction if the person has been infected with TB bacteria. In most people who have TB infection, the immune system will recognize the PPD because it is derived from proteins that are excreted by M. tuberculosis growing in specialized media under standardized conditions. PPD is diluted to standard concentration and potency in FDA-approved testing solutions. It takes 2 to 8 weeks after initial infection with TB bacteria for the immune system to be able to react to PPD and for the infection to be detected by the TB skin test.
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Advantages and disadvantages of the TB skin test
Advantages
- Simple to perform (e.g., no laboratory equipment required)
- Low cost
- No need for phlebotomy
- Well-established definitions of TB skin test conversions
- Legacy of decades of clinical and epidemiological research
Disadvantages
- Requires trained personnel to administer and interpret
- Requires correct refrigeration and an inventory plan for the skin test solution
- Requires two or more patient visits
- Previous BCG vaccination or infection with nontuberculous mycobacteria can cause false-positive results
- Concurrent infections can cause false-negative results
- Rare adverse effects
- Can cause booster phenomenon
- Subject to biases and errors with TB skin test placement and reading
Who can administer and read TB skin tests?
The TB skin test should be placed (administered) and read by a designated, trained health care provider. Consult with your state and local public health authorities to determine who is authorized to place and read TB skin tests in your state.
TB skin test training materials
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Training is essential for health care providers to gain proficiency in the administration and interpretation of the TB skin test.
CDC has free training materials on reading and administering the TB skin test, including a fact sheet, wall chart, and video. Materials are available for download or to order (within the United States).
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