When performing the repeated open application test (ROAT) for allergic dermatitis, a minimum 10-day application period is needed to be confident that a positive result will be detected, according to a new prospective study out of France.
Researchers found that nearly all positive results appear within that time frame, which is shorter than the 15 days currently recommended by the European Society of Clinical Dermatology.
"Our study shows that a minimum of 10 days is necessary and probably sufficient to achieve a positive ROAT," the authors write in the study published online April 5 in Contact Dermatitis.
ROAT seeks to mimic repeated exposure by applying potential allergens twice per day for up to 2 weeks, though sometimes as long as 4 weeks in cases of high levels of suspicion. This is because the test can give a negative result after 1-2 weeks despite the existence of a contact allergy. However, extended periods of testing can be difficult for patients. It can involve more office visits to apply the allergen, and patients may be uncomfortable with the test itself or the need to interrupt antihistamine or other treatments.
Still, "missing potentially 10% of positive results takes away from somebody who's really trying to put a lot of effort into figuring out something, because by the time someone reaches the point where they're doing this test, they've already got a really frustrating and recurrent rash," said Sonya Kenkare, MD, who was not involved with the French study but provided independent comment on it for
