Interpretation of patch test reactions

Score	Interpretation	Tips and advice
–	Negative reaction
? or +/–	Doubtful reaction, faint erythema	Caution with interpretation, especially with less common allergens. Consider repeat testing or follow-up with ROAT testing.
+	Weak reaction, erythema, slight infiltration	Erythema should be palpable and occupy >50% of patch test site.
++	Strong reaction, erythema, infiltration, vesicles	Look for microvesicles to occupy at least 50% of the patch test site.
+++	Extreme, bullous, ulcerative	Confluent vesicles.
IR	Irritant reactions	There is a broad range. Mild irritant reactions have a glazed appearance. Moderate reactions are follicular (pustular in atopics). Extreme reactions can be ulcerative.
NT	Not tested

ROAT: repeated open application test.

Graphic 65159 Version 2.0