Atopy patch tests may identify patients at risk for systemic contact dermatitis

BACKGROUND: A subset of patients with positive patch tests demonstrates systemic contact dermatitis (SCD) upon ingestion or inhalation of the allergen. Concern has been raised about the use of patch tests for protein allergens (APTs) to detect SCD in atopic dermatitis (AD) patients. METHODS: We present atopy patch test (APT) data for 97 people. We reviewed APTs and tests for antigen-specific immunoglobulin E (IgE) to the same allergen in pediatric AD patients. We compared the frequency of APTs as a function of age in AD patients. To study the irritancy potential of APTs, we prospectively tested consenting non-AD dermatitis patients undergoing evaluation for allergic contact dermatitis and healthy controls to an APT panel. RESULTS: APT demonstrated fewer positive results than serum-specific IgE or skin prick tests to the same allergen. Positive APT to food was more common in children under 3 years, whereas positive APT to aeroallergens were more common in teens and adults. Only positive APTs to dust mite were significantly more common positive in subjects without AD. CONCLUSION: Our aggregate findings suggest that most APTs, but not dust mite, behave like conventional patch tests to low-potency allergens. They are more likely to be positive in patients with chronically inflamed skin and to identify allergens that cause SCD. The higher prevalence of APT positivity to foods in young children is consistent with food allergy as a trigger of AD (also known as SCD) being more common in children than adults. Positive APTs define patients who may have SCD; negative APTs may guide elimination diets.