Interpretation of patch test results
Visual imprints on the skin from each chamber + a slight erythema from the frames should be visible as a sign of good occlusion. Reading of the test is preferably performed at day 3 or 4 plus at day 7 after test application for haptens that may show delayed reactions. At day 3, a weak erythema from the frames might be present in patients with sensitive skin. Some clinics prefer to add an initial reading when the tape units are removed. If this is made, allow initial skin irritation from the backing tape and the foam frame tape to subside, as well as reduction of the visual imprint on the skin due to the high skin occlusion of the chambers.
Use the Reading Plate for IQ Ultra™/ IQ Ultimate™ to facilitate the reading. For the interpretation of the test result the following scheme can be used:
IR Irritant reaction
- Faint macular - No infiltration
- Homogenous erythema
Photopatch tests are graded similarly by just adding the prefix Ph. The relevance of the reaction should be assessed and recorded as present, past or unexplained. In doubtful cases, a repeated open application test (ROAT) is recommended. The test material is then applied to the skin of the antecubital space of the upper arm twice daily for a week. In most cases of contact allergy, an itching papular dermatitis will develop within a few days.