Delayed Patch-Test Reading After 5 Days: An Update From the Mayo Clinic Contact Dermatitis Group

Area of Science:

• Dermatology
• Allergology
• Contact Dermatitis

Background:

• Delayed patch-test readings beyond day 5 have been used to detect reactions to metals and topical antibiotics.
• Previous research indicated the value of extended patch-test reading intervals.

Purpose of the Study:

• To determine which allergens benefit most from late patch-test readings (after day 5).
• To compare current findings on delayed patch-test reactions with prior studies.

Main Methods:

• A retrospective analysis of 298 patients undergoing metal and corticosteroid series patch testing.
• Patch tests were read on days 3, 5, and between days 7–14, with all reactions documented at each interval.

Main Results:

• Late readings (after day 7) were particularly useful for identifying reactions to metals (gold, cobalt, beryllium, palladium).
• Specific preservatives (dodecyl gallate, propolis) and the antibiotic neomycin also showed utility with late readings.
• No new delayed reactions were observed for bacitracin, p-phenylenediamine, or topical corticosteroids in this cohort.

Conclusions:

• Extended patch-test reading intervals are beneficial for detecting delayed hypersensitivity to certain metals and preservatives.
• The findings align with previous research, reinforcing the importance of late readings for specific allergens.
• Further investigation into delayed reactions to other substances may be warranted.