Huanren Lab

 1. Introduction to the background of the patch test

The patch test has been used in clinical practice for more than 100 years, and the reliability of assisting in the diagnosis of contact dermatitis and detection of contact allergens has been fully proven clinically. In developed countries such as Europe and the United States, patch testing technology is one of the basic skills that dermatologists must possess. Spot test In addition to the macromolecular substances used in atopic patch tests, most allergens are small molecule chemical substances, which are widely present in our production and living environments, such as clothing, jewelry, household goods, toiletries, production materials, labor tools, cosmetics, medicines, foods and additives.

2. Principle of patch test

The PatchTest is a simple and reliable method to determine allergens in patients with dermatitis and eczema. When the patient is allergic to the skin or mucosa contact allergen, any part of the body surface that has the same antigenic substance similar to the same allergen or chemical structure, will soon appear in the contact site of skin inflammation, which is allergic contact dermatitis. The patch test uses this principle to artificially configure suspicious allergens to a certain concentration, place them in a special small room and apply them to the covered area of ​​the human body (often on the back and forearm flexing side). After a certain period of time, it is determined whether the test substance is an allergen (i.e., an allergen) based on whether there is a positive reaction. If substances that cause allergies in the body can be found, they can be prevented and treated earlier.

The patch test is a skin-induced test. If the allergen tested is irritating to the skin, it can also induce irritating dermatitis. Therefore, the patch test should avoid irritating reactions as much as possible. First, try to choose mature allergens sold in the market for testing . The substances brought by the patient themselves must be familiar with their physical and chemical properties. Do not directly test substances that are known to be irritating, such as acids, alkalis, salts and corrosive substances. Secondly, even allergens sold on the market will have irritating reactions due to factors such as testing time and skin status. For example, people with high temperatures, humid environments, sweating, tender skin or patients with atopic dermatitis are prone to irritating reactions, and attention must be paid to distinguish them from real allergic reactions. Similarly, since patch tests are skin-induced tests that can cause rapid-hair contact reactions such as contact urticaria or even severe systemic allergic reactions, patients with such medical history should not use allergens that may cause rapid-hair allergies for patch tests.

3. Operation steps for patch test:

1) First uncover the tape layer and blister layer of the speckle tester.

2) Extrude allergen from the syringe or vial and place it in the speckle tester.

3) The principle of liquid allergy requires that filter paper be placed in the speckle tester in advance (filter paper has been added to the Ruimin speckle tester), and then allergen is added driply.

4) The amount added to the allergen is to be so that the tester can contact the skin without overflowing the spot (about 25ul, the size of solid mung beans, 1 drop of liquid).

5) After the allergen is added, close the tape layer of the speckle tester and the blister layer. It can be stored at 2~8℃ for 2 weeks, or directly apply the tape with the allergen added to the skin of the subject's upper back (from bottom to top, press for 5 seconds), and use a marker to mark the core chamber.

6) After applying the patch for 48 hours, remove the tape layer of the spot tester, observe the skin manifestation of the patch on the back after 30 minutes, and observe the skin manifestation of the patch on the back again after 24 to 72 hours.

Notes:

1. Do not clean during the test (use a waterproof spot tester to perform shower) or scratch the patch area.

2. Do not exercise vigorously to avoid dislocation of the speckle tester; avoid sunlight exposure to the patch site; avoid oral hormone drugs (oral antihistamine drugs have no effect) during the test.

3. Try to avoid exercise and reduce sweating. If you cannot avoid strenuous exercise or severe sweating, you can use tape to fix it yourself.

4. Pay attention to keeping the marking points (for positioning) around the spot tester clear. If the marking points are blurred or disappear, please use a marker to paint the marking points clearly in time to facilitate the interpretation of the results.

5. If the skin reaction on the patch test site is strong, especially pain or burning, remove the spot tester in time and take photos of the patch site, and return to the hospital for medical treatment in time.

4. Indications for patch test

The patch test is suitable for all clinical tests of contact allergies suspected of the presence of contact allergens, including: ① Allergic contact dermatitis, patients with eczema with a clear history of contact suggesting that they may be allergic contact dermatitis; ② Patients with atopic dermatitis; ③ Various types of eczema dermatitis, especially seborrheic dermatitis, stagnant dermatitis and other acute attacks; ④ Contact dermatitis syndrome (systemic contact dermatitis): manifested as irregular vesicular eczema with hands and feet, baboon syndrome-like rash or pancreatic eczema; ⑤ Although there is no clear history of contact, dermatitis occurs in special areas, such as dermatitis eczema in exposed areas such as hands, face, neck, etc.; ⑥ When stagnant dermatitis, chronic eczema and other chronic recurrent skin diseases are suspected of secondary external drug contact allergies; ⑦ When it is necessary to distinguish allergic contact dermatitis from irritating contact dermatitis; ⑧ When drug-induced dermatitis, food allergies, etc. are suspected to be caused by late-onset allergic reactions (drug patch tests and atopic patch tests should be carried out separately).

5. Contraindications for application of patch tests

① It is known that allergens are allergic to the tested. For example, patients with hair dye dermatitis who are allergic to phenylenediamine should not test p-phenylenediamine; patients with positive penicillin dermatitis test should not test penicillin; ② Due to the unclear impact on pregnancy and breastfeeding, pregnant women and breastfeeding women cannot conduct patch tests; ③ Patients with rapid hair contact reactions, such as contact urticaria, especially in patients with severe systemic allergic reactions (allergies) cannot conduct suspicious allergen patch tests; ④ Substances known to be toxic, harmful and significantly irritating to the skin, such as acids, alkalis, salts, corrosive chemicals, etc. cannot conduct patch tests directly; ⑤ Patients who have no ability to control behavior or patients who cannot guarantee the patch test conditions cannot conduct patch tests.

6. Spot test interpretation standards