A major question in patch testing is when to perform the final reading. Our current standard practice is to place patches on day 1, remove them on day 3, and perform readings on days 3 and 5. For certain allergens, another reading is performed sometime from days 7 to 14≥.
The aim of the study was to identify allergens with positive reactions on day 5 that were negative on day 7 or later and allergens with negative reactions on day 5 that were subsequently positive on day 7 or later.
We reviewed records of patients who underwent patch testing from January 2007 to December 2016 at Mayo Clinic with readings on day 5 and day 7 or later.
In total, 131 allergens had positive reactions on day 5 that were negative on day 7 or later, and 58 allergens had negative reactions on day 5 that were positive on day 7 or later. Twenty-five allergens had significantly higher reaction rates on day 5 than day 7 or later. Our standard practice is to perform readings on days 3 and 5 and on days 3, 5, and 7 or later for series containing metals. Readings on days 3, 5, and 7 or later should also be considered for acrylates.