Isolated late cutaneous reactions to allergen skin testing in children

Occasionally parents report a reaction developing at the site of an allergen skin test several hours after application of the test, despite there having been no immediate reaction. The medical literature contains little information regarding isolated late reactions (ILRs) to allergen skin testing.

The goal of this project was to determine the incidence of ILRs in children undergoing allergen skin testing.

Prick and intradermal (ID) skin testing was performed for routine clinical indications in an allergy clinic. Children with a positive histamine control, and at least one negative immediate reaction to allergen skin testing were enrolled in the study. The parents were given detailed instructions to examine the skin test sites 6 hours later, and to record the size of any erythematous indurated sites. Circles of various diameters were included on the report form to assist the parents' size estimates.

Fifty-seven children enrolled in the study and 50 returned the forms. No patients reported ILRs to prick skin tests. Eighteen of the 50 respondents reported 40 ILRs to ID tests, of > or = 5 mm diameter; 7 of these were > or = 10 mm. The most common allergen causing ILR was cockroach, accounting for 20% of the ILRs. Each of the other allergens also caused ILRs. The clinical history did not show a definite correlation of symptoms with exposure to the allergens causing ILRs, although all 14 patients with ILRs to indoor allergens had year-round symptoms. There was no correlation between the incidence of ILRs and age, gender, or diagnosis of asthma.

ILRs to allergen skin testing occurred in 36% of pediatric allergy clinic patients. The clinical significance of such reactions is unknown.