title: Delayed patch test reactions at days 7 and 9.
abstract: 403 consecutive patients were examined on days 2, 4, 7, and 9 following application of patch tests. Late positive reactions, i.e., those which manifested after day 4, were seen in 29 patients (7.2%). The allergens which most commonly produced late positive reactions were neomycin (7), potassium dichromate (4), and cobalt (3). Paired patch test readings on days 4 and 7 were more reliable than those on days 2 and 4. If only 1 patch test reading were performed, a single reading on day 4 would have been most useful. The reading on day 9 proved to be of limited value. Of 11 patients who were retested after an interval of more than 6 months, 7 showed earlier eliciting reactions, which may have been due to active sensitization.
authors.affiliation: University Department of Dermatology, Royal Liverpool Hospital, UK.
authors.forename: A W
authors.initials: AW
authors.lastname: Macfarlane
authors.forename: R K
authors.initials: RK
authors.lastname: Curley
authors.forename: R M
authors.initials: RM
authors.lastname: Graham
authors.forename: M S
authors.initials: MS
authors.lastname: Lewis-Jones
authors.forename: C M
authors.initials: CM
authors.lastname: King
mesh_terms: D003877:Dermatitis, Contact / Q000209:etiology*; D006801:Humans; D010328:Patch Tests; D013997:Time Factors