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Patch tests are tests to detect allergens that sensitize a person. They are used to detect skin (contact) allergies. Patch tests are used to confirm an initial diagnosis made by an allergist doctor. They also make it possible to determine the severity of allergies, and thus allow you to select the appropriate dose of the drug and the duration of its use.
Types of allergy tests
People can have three types of allergies: food, inhalation, and contact (skin) allergies. In the case of food and inhalation allergies, it is performed tests by puncturing the skin and introducing a small amount of the allergen (intradermal tests) and blood tests. Contact allergies are diagnosed on the basis of patch tests. Patch test it includes a set of allergens such as metals (chromium, cobalt, vanadium, titanium, molybdenum, nickel), preservatives, fragrances, drugs (antibiotics, including neomycin), adhesives, rubbers, synthetic and natural resins, dental materials and dyes. The patient can also bring a substance that he suspects to be allergic to him – for example a cosmetic. Down patch tests caustic and irritating substances are not used.
How are patch tests performed?
Epidermal patch test performed on the skin of the back. It consists in the fact that the doctor soaks a tissue specially designed for this purpose with an allergen or puts an allergen paste on a special patch. The tissue paper or patch is stuck to the skin on the patient’s back for 48 hours. The skin must be dry, clean and free from hair. Slices (or tissue paper) are glued every 2 cm. The reaction (back skin condition) is checked again 72 and 96 hours after the allergen has been applied – some substances give a delayed allergic reaction at the point of contact with the skin.
For 48 hours, when they are stuck to the skin of the back patches / papers soaked in the allergen, the patient should avoid strenuous exercise so as not to sweat the skin. You should also not take a shower so as not to wet the patches with water.
Indications for performance for patch tests
Patch tests are used to confirm the initial diagnosis of the allergist. If he suspects a patient has a contact allergy, the patch test will not only help confirm it, but also determine exactly which substances of a given patient sensitize and to what extent the allergy is severe. This will allow for the appropriate selection of drugs, their dose and duration of treatment.
Patch tests is performed when skin contact allergies are suspected.
Symptoms qualifying the patient to be carried out epidermal flake testsh, to:
- chronic itchy skin lesions;
- atopic eczema in the form of redness, peeling and dry skin;
- allergic contact dermatitis;
- sweat eczema in the form of itching and skin blisters on the skin of the hands and soles of the feet;
- nematode eczema, i.e. tiny spots and blisters fusing into coin-shaped clusters;
- eczema hematogens;
- occupational eczema, which most often occurs on the skin of the hand;
- seborrheic dermatitis that occurs on the face, in the area of the sternum and in the area between the shoulder blades;
- photodermatoses, i.e. skin changes appearing on parts of the body that have been exposed to the sun (UV radiation).
Interpreting the results of the patch test
Results of epidermal patch tests is interpreted on a plus scale of 0 to three pluses. At least 2 pluses are considered a positive result.
- Result 0 means no reaction,
- + means erythema,
- ++ indicates the appearance of erythema and papules,
- +++ means the appearance of erythema, papules, vesicles and edema.
In order to eliminate false allergic reactions it is used positive with histamine – it must give a positive skin reaction. If this is not the case, the test is not eligible for evaluation.
Negative sample performed with the use of saline. It should be neutral – if this is not the case, patch test it is considered unreliable.
How to prepare for the patch tests?
For epidermal patch tests prepare properly. Four weeks before the move patch tests for allergies, stop using topical steroids and stop using ketotifen in the place where the allergen papers will be glued (i.e. on the skin of the back and – possibly – on the forearms).
Two weeks before execution patch tests the use of second-generation antihistamines should be discontinued.
Three days before the move patch test first generation antihistamines should be discontinued, as well as calcium, vitamin C and rutin should not be used, which affect the permeability of blood vessels and increase the allergic reaction.
Inhalation drugs (bronchial and intranasal) and skin care creams have no effect on the result patch test.
For the patch test you should report on an empty stomach.
Patients who have a hairy back and skin on their forearms before with a patch test should get rid of hair.