Process
Prior to testing, avoid taking oral prednisone or other immunosuppressive medications for at least a week prior to testing. Steroid inhalers are OK to use. Avoid sunlight/sunburn for at least a week on the back as this may suppress positive reactions. Antihistamines such as diphenhydramine (Benadryl) or cetirizine (Zyrtec) are permissible prior to and during testing.
Application of the patch tests will take about half an hour, though many times the overall appointment time will be longer as your provider will take an extensive history. Tiny quantities of 25 to ~150 materials (allergens) in individual square plastic or round aluminium chambers are applied to the upper back. They are kept in place with special hypoallergenic adhesive tape. The patches stay in place undisturbed for at least 48 hours. Getting the back wet during patch testing should be avoided (no shower). Vigorous exercise or stretching may disrupt the tests.
At the second appointment, usually 48 hours later, the patches will be removed. Sometimes further patches are applied. The back is marked with an indelible black felt tip pen or other suitable marker to identify the test sites and a preliminary reading is done. These marks must be visible at the third appointment, usually 24–48 hours later (72–96 hours after application). The back should be checked and if necessary re-marked on several occasions between the 2nd and 3rd appointments. In some cases, a reading at 7 days may be requested, especially if a special metal series is tested.
Read more about this topic: Patch Test (medicine)
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