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Patch Testing

See Also
1. Allergy Test
Indications
1. Allergic Contact Dermatitis (Type 4 Hypersensitivity)
Efficacy: Evaluating Allergic Contact Dermatitis
1. Test Sensitivity: 70%
2. Test Specificity: 70%
Technique
1. Place drop of each diluted agent in patch test chamber
2. Apply patch to non-irritated, clean skin of back
3. Outline each patch outline with pen
4. Label agent locations on skin and in medical record
5. Remove patch in 48 hours
6. Measure skin reaction (see below)
Interpretation of skin test
1. Erythema: 1+
2. Edema or Vesicles involve <50% of patch area: 2+
3. Edema or Vesicles involve >50% of patch area: 3+
False positive causes (consider if multiple positives)
1. Hyperirritability of skin
2. Contaminant irritant or allergan on tested skin
3. Reaction to tape holding patch in place
4. Irritant Contact Dermatitis
  1. Reaction resolves more quickly than in allergy
  2. Burning sensation contrasted with itching in allergy
  3. Sharply demarcated reaction
References
1. Mydlarski in Middleton (1998) Allergy :
2. Riedl (2003) Am Fam Physician 68:1781

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This page was written by Scott Moses, MD. This page was last revised before 5/10/08, prior to consistent tracking of revision date. This page was last published on 6/1/2008. Please send comments and questions to the editor. Contact information may be found on the page About the Family Practice Notebook. These pages are best viewed with Microsoft Internet Explorer 6.0.