The choice of the best application of the patch test site is the result of the classical works of Magnusson. It is the high dorsal para-vertebrale region which offers qualities flat surface and grip ensuring good reproducibility of tests.
A few points of detail
Tests are applied to sides of the spine at least 5 cm of part and sides of the midline. They are not placed in the part of the near back of the neck for reasons of discomfort and lower adhesion which would result in a risk of detachment of test equipment and also common irritation of the integument. The region that covers the shoulder blades is favourable. If the tests are more numerous, the lowest areas are also suitable.
These application sites are chosen uniformly around the world. They are not exclusive. If necessary, other sites could be used:
the face inner thigh, the face of the extension of the arm, the face of flexion of the forearm. This choice may be dictated in the event of extreme Hairiness of the back.
On the other hand, it would be interesting sometimes to perform a patch test on a neighbouring territory of the place where the allergic contact eczema is developed. Indeed, it can happen that a test gives a false negative response when it is made too large distance from initial of eczema headquarters, while a nearby test gives a positive response.
An attempt to explain such an unconformity, is used to the concept of memory local or regional memory of the integument. It uses only exceptionally this variation when applied in the dorsal region tests are negative and this negativity seems NET unconformable with the clinic.
In the case of eczema of the eyelids, is used more palpebral test, because of the discomfort it provides to the patient.