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Some skin tests are less accurate than others. A significant number of patients with active tuberculosis have negative tuberculin skin tests (called PPD or Tine tests). Tetanus immunization (vaccine) can cause false positive results for diphtheria (Schick test). Tests for food allergies may be less accurate than disease antigen testing.
Other factors that can affect the test results include:
- Where on the body the test is performed (the arm reacts differently than the back)
- The time of day (morning tests react differently than afternoon tests)
- Proximity (closeness) to other tests
- Antihistamines can cause a false negative test (negative results when the antigen should show reaction)
- Old antigens are used
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