Patch Test
A standardised epicutaneous diagnostic procedure used to identify type IV (delayed) hypersensitivity reactions to contact allergens.
Full Definition
Patch testing is the gold-standard investigation for allergic contact dermatitis, involving the application of standardised allergen preparations to the upper back under occlusive chambers for 48 hours, with readings taken at 48 and 96 hours. Results are graded according to the International Contact Dermatitis Research Group (ICDRG) scale (ranging from negative through doubtful reaction to strong positive). Editors should be alert to the distinction between 'patch test' (for contact allergy, delayed hypersensitivity) and 'prick test' or 'skin prick test' (for immediate IgE-mediated allergy). The two-word form 'patch test' (noun) and 'patch testing' (gerund/noun) are standard; 'patch-test' as a hyphenated compound verb is acceptable (e.g., 'the patient was patch-tested').
Usage
Usage note: Two-word noun form: 'patch test.' Hyphenated verb form: 'patch-test.' Never confuse with 'prick test' (SPT), which tests IgE-mediated immediate hypersensitivity.
In Context
- "Patch testing using the European baseline series identified a strong positive reaction to nickel sulfate at D4 reading." — Allergy and dermatology investigation report
- "The author uses 'patch test' and 'prick test' interchangeably — these are distinct procedures and must not be conflated; a query has been raised." — Copy-editing query to author