title: The relevance of 7-day patch test reading.
abstract: BACKGROUND
  Patch test readings are usually performed on day 2 (48 hours) and day 4 (96 hours). However, reports in the literature identify delayed allergy to metals, corticosteroids, antibiotics, some preservatives, acrylic and methacrylic monomers and p-phenylenediamine.
  
  
  OBJECTIVE
  The aim of our study was to identify the benefit of performing a day 7 (168 hours) reading to identify relevant late positive reactions.
  Two hundred three consecutive patients were patch tested to the British Society for Cutaneous Allergy standard series with additional test series selected according to clinical history and applied at the same time.
  
  
  RESULTS
  Twenty-six patients (12.8%) had new positive reactions on day 7 (168 hours), with 28 relevant positive reactions to 21 allergens. These included mercury 0.5% (2/26); cobalt chloride 1% (2/26); colophony 20% (2/26); disperse blue mix 106/124 1% (2/26); preservatives (4/26) that included Methylchloroisothiazolinone/methylisothiazolinone, sodium metabisulfite, and diazolidinyl urea; fragrances (7/26); and gentamycin sulfate 20% (1/26).
  
  
  CONCLUSIONS
  These results confirm findings in the literature and support the argument for performing a day 7 reading (168 hours) to identify relevant late positive reactions.
authors.affiliation: From the Department of Dermatology, St Vincent's University Hospital, Dublin, Ireland.
authors.forename: Eleanor
authors.initials: E
authors.lastname: Higgins
authors.forename: Paul
authors.initials: P
authors.lastname: Collins
mesh_terms: D003035:Cobalt / Q000009:adverse effects; D017449:Dermatitis, Allergic Contact / Q000175:diagnosis* / Q000209:etiology*; D005188:False Negative Reactions; D005839:Gentamicins / Q000009:adverse effects; D006801:Humans; D008628:Mercury / Q000009:adverse effects; D010165:Palladium / Q000009:adverse effects; D010328:Patch Tests / Q000379:methods*; D010476:Perfume / Q000009:adverse effects; D012116:Resins, Plant / Q000009:adverse effects; D013997:Time Factors; D014508:Urea / Q000009:adverse effects / Q000031:analogs & derivatives
chemical_list: D005839:Gentamicins; D010476:Perfume; D012116:Resins, Plant; D003035:Cobalt; D010165:Palladium; C013893:rosin; D014508:Urea; C018021:cobaltous chloride; D008628:Mercury; C044982:diazolidinylurea; C008756:palladium chloride