Patch tests are commonly used to aid in the diagnosis of allergic contact dermatitis. A patch test may assist in identifying the specific substance or substances causing allergic inflammation of your skin.
Patch testing involves applying small amounts of various allergens onto small squares on a larger patch, and the adherence of the patch or patches onto the skin. Patches are typically placed on an individual’s back and worn for 48 hours. The test area is usually examined for signs of an allergic reaction at 48 and 72-96 hours following initial patch application.
At the Australian Allergy Centre we use the TRUE Test® patch test – a ready to use patch test that screens for sensitivity to 80% of the most common causative agents of contact dermatitis. Substances tested include nickel, fragrances, parabens and a range of other allergen components commonly found within jewellery, metal, cosmetics, skin care products, soaps, fragrances, hair shampoos, conditioners and dyes, topical medications, creams and ointments, adhesives and bandages, fabrics, inks, household disinfectants and industrial products, and other everyday materials (Smart Practice Dermatology, 2012).
A positive reaction generally becomes red and itchy at the test site. Swelling or a small fluid-filled blister may develop. Positive reactions usually become apparent by 72-96 hours. Occasionally reactions can take longer to develop – up to two weeks.
At the Australian Allergy Centre patch testing is available for $220, with a Medicare rebate of $53.10. All consultations with our doctors are bulk-billed.
Care of your patch test
To ensure the most accurate interpretation of your patch test, it is important to minimise exposure of the test area to moisture while the patch is in place. Avoid wetting the area when showering or bathing, and participating in activities which may cause you to sweat excessively such as sunbaking and exercising. After patch removal it is advised you continue to keep the area as dry as possible, however showering is permitted. Please note, some substances may stain the skin; this is normal and stains will wash off after a couple of days with showering or bathing. Scrubbing of the area is not recommended before your final review.
The administration of oral corticosteroids, and application of topical corticosteroids to the test area (upper back), must be ceased two weeks prior to patch testing, and continue to be avoided for the duration of the patch test and review period. This is important as such pharmacological treatments may suppress or alter a positive reaction, and interfere with accurate test interpretation. It is common to experience burning and itching sensations on and around the test area, however scratching and rubbing of the test area should be avoided.
Smart Practice Dermatology. 2012. T.R.U.E Test Reference Manual. Accessed 31 July, 2015, http://www.truetest.com/TRUE_TEST_Reference_Manual_Final_2012.pdf