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A visual scale for patch test reactions.

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Source: Spiewak R. Patch testing for contact allergy
and allergic contact dermatitis. Open Allergy J 2008; 1: 42-51.
(c) Radoslaw Spiewak, reprinted with permission.”

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For the interpretation of the test result the following scheme can be used;

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- Negative reaction

? Doubtful reaction

+ Weak reaction (non-vesicular)

++ Strong reaction (oedematous or vesicular)

+++ Extreme reaction (ulcerative or bullous)

IR Irritant reaction

NT Not tested

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Photopatch tests are graded similarly by just adding the prefix Ph. The relevance of the reaction should be assessed and recorded as present, past or unexplained. In doubtful cases, a repeated open application test (ROAT) is recommended. The test material is then applied to the skin of the antecubital space of the upper arm twice daily for a week. In most cases of contact allergy, an itching papular dermatitis will develop within a few days.