Patch Testing Guide

Test Preparation

The patch test panels are prepared by filling small metal cups with the allergens to be tested. The panels may be customized for a particular person, or standardized. The TRUE test is a standard panel of 24 allergens pre-loaded onto paper tape.. Daniel More, MD

Test Preparation Completion

The process is repeated for all allergens to be tested. Patch testing may be performed to dozens of allergens, depending on the possible causes of a person's contact dermatitis. Your physician will determine the actual number of tests needed.. Daniel More, MD

Test Placement

The patches are then placed onto the person's back, with the chemicals against the skin. To prepare for the test, a person should have clean skin and have recently bathed. The skin should not be cleaned with rubbing alcohol, which may irritate the skin.. Daniel More, MD

Test Placement Completion

The procedure is repeated until all of the patches are placed, usually on the back. Patch tests are often placed on Mondays, as the results will be read at 48 and 96 hours after placement. The tape cannot get wet during this time, so bathing is limited.. Daniel More, MD

Patch Test Removal

The patch tests are removed after 48 hours, and an initial reading of the test site is performed. A test is considered positive if bumps, blisters or swelling are at the individual sites. Usually, redness alone is not a positive test.. Daniel More, MD

Removing the Patch Tests

The tape itself may cause some irritation, so the test panels are removed and the initial reading is performed about 30 minutes later. A positive test site may be very itchy, but it is important not to scratch the site, as this may alter the results.. Daniel More, MD

Reading the Results

A second reading of the results occurs at 72 to 96 hours after initial placement of the patch tests. It may take this long for some results to develop. The sites may remain red and itchy for days, but hydrocortisone cream can relieve the symptoms.. Daniel More, MD

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