title: Delayed readings of a standard screening patch test tray: frequency of "lost," "found," and "persistent" reactions.
abstract: BACKGROUND
  Several studies have shown that patch test results vary depending on the time at which the patch test sites are evaluated.
  
  
  OBJECTIVE
  This study aims to determine the frequency of "lost," "found," and "persistent" reactions to a standard screening tray by comparing initial and delayed readings of the same patch tests.
  
  
  METHODS
  We performed a retrospective review of patch test reactions for 587 patients tested with the standard screening tray at The Cleveland Clinic Foundation (Cleveland, OH) between January 1, 1988, and December 31, 1991, for which an initial day-3 and delayed day-4 to day-8 readings were available.
  
  
  RESULTS
  For the 587 patients, we identified 81 found (15%), 342 persistent (62%), and 127 lost (23%) reactions, for a total of 550 reactions (100%). The three most common found reactions were to neomycin sulfate (n = 19; 53%), p-phenylenediamine (n = 10; 29%), and thiomersal (n = 10; 18%). The three most common persistent reactions were to thiomersal (n = 41; 73%), nickel sulfate (n = 33; 73%), and quaternium 15 (n = 32; 74%). The three most common lost reactions were to balsam of Peru (n = 14; 39%), benzoyl peroxide (n = 12; 63%), and nickel sulfate (n = 9; 20%).
  
  
  CONCLUSIONS
  Two patch test readings are necessary, followed by a final interpretation.
authors: Department of Dermatology, Rheinisch-Westfälische Technische Hochschule Aachen, Aachen, Germany.
authors: H
authors: H
authors: Dickel
authors: J S
authors: JS
authors: Taylor
authors: P
authors: P
authors: Evey
authors: H F
authors: HF
authors: Merk
mesh_terms: D017449:Dermatitis, Allergic Contact / Q000175:diagnosis*; D006801:Humans; D010328:Patch Tests / Q000592:standards*; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D013997:Time Factors