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Patch Testing
Aka: Patch Testing, Patch Test
- See Also
- Allergy Test
- RadioAllergoSorbent Test
- Regional Allergy Screening
- Indications
- Allergic Contact Dermatitis (Type 4 Hypersensitivity)
- Mechanism
- Contact Dermatitis is a delayed T cell-mediated response (Type 4 delayed Hypersensitivity)
- Most common contact allergans
- Rhus Dermatitis (e.g. Poison Ivy)
- Nickel Allergy
- Cosmetic allergy
- Rubber product allergy (Latex Allergy)
- Efficacy: Evaluating Allergic Contact Dermatitis
- Test Sensitivity: 70%
- Test Specificity: 70%
- Technique
- Place drop of each diluted agent in Patch Test chamber
- Apply patch to non-irritated, clean skin of back
- Outline each patch outline with pen
- Label agent locations on skin and in medical record
- Remove patch in 48 hours
- Measure skin reaction (see below)
- Approach: Interpretation of skin test
- Erythema: 1+ (Mild)
- Accuracy 20%
- Edema or Vesicles involve <50% of patch area: 2+
- Edema or Vesicles involve >50% of patch area: 3+
- Accuracy 90%
- Causes: False Positive (consider if multiple positives)
- Hyperirritability of skin
- Contaminant irritant or allergen on tested skin
- Reaction to tape holding patch in place
- Irritant Contact Dermatitis
- Reaction resolves more quickly than in allergy
- Burning sensation contrasted with itching in allergy
- Sharply demarcated reaction
- References
- Chang (2018) Am Fam Physician 98(1): 34-9 [PubMed]
- Mydlarski in Middleton (1998) Allergy, Mosby, p. 1141-2 [PubMed]
- Riedl (2003) Am Fam Physician 68:1781-90 [PubMed]