Is allergen testing ＂futile＂, or can it really find out the ＂culprit＂ of sensitization？

　　Photo courtesy of vision china

　　Allergy survey ②

　　Generally speaking, the results of allergen detection combined with medical history are relatively reliable. Allergic people don’t need to do allergen testing regularly, just wait until they have allergic symptoms but are not sure about allergens. In addition, they should choose professional and qualified institutions for testing.

　　liu yongsheng

　　Director of Dermatology, Aviation General Hospital

　　Is allergen testing reliable?

　　This is one of the most frequently asked questions by Hu Liang, a pediatrician in Changchun Children’s Hospital. Many people suffer from allergies. In order to find allergens, they went to the hospital for allergen testing, and found that they were "lonely". The test results did not seem to be very helpful to control allergies.

　　So, what are the main methods of allergen detection? How effective are these methods? Why do some people feel that they have "tested in vain"? Around these problems, the reporter of Science and Technology Daily interviewed relevant experts.

　　Identifying allergens is the key to controlling allergies.

　　Allergic diseases are also called allergic diseases, commonly known as allergies. According to the data, it is estimated that by 2050, about 4 billion people in the world will suffer from allergic asthma, allergic rhinitis and atopic dermatitis, and allergy has become the sixth largest chronic disease in the world.

　　Allergy is closely related to allergens.

　　Jiang Weihong, chief physician of the Department of Otolaryngology, Head and Neck Surgery, Xiangya Hospital, Central South University, said that allergens enter the human body through oral administration, inhalation, contact or injection, and bites, and allergic reactions occur in the human body. Therefore, if you want to control allergies, the key is to diagnose and determine allergens. Only by clarifying the cause of allergy can we correctly choose the treatment plan.

　　However, there are many kinds of allergens in life, the most common are food allergens and inhalation allergens, and some are contact allergies.

　　So, how can we "find out" the allergens that really cause allergies? This requires allergen testing.

　　Liu Yongsheng, director of dermatology department of Aviation General Hospital, said that patients with allergies will produce specific IgE in their bodies after being exposed to allergens, and then the specific IgE will enter the circulatory system and be transported to all parts of the body, where it will combine with mast cells and basophils. Mast cells and basophils combined with specific IgE will meet and combine with allergens again, and then trigger mast cells and basophils to release inflammatory factors, such as histamine, which can directly lead to allergic inflammation and cause symptoms of type I allergic reaction in human body.

　　"So, what is usually called allergen testing is specific IgE." Liu Yongsheng said.

　　Different detection methods have their own advantages and disadvantages.

　　Liu Yongsheng introduced that the methods of allergen examination can be roughly divided into intradermal test or prick test, serum test, patch test and provocation test.

　　The principle of intradermal test or prick test is to let a certain amount of allergens enter the skin through a specific way, and then observe whether the allergens will cause allergic reactions, and judge the degree of allergies according to the degree of local skin allergic reactions, which is commonly known as "prick test". Liu Yongsheng said that this method has the advantages of simplicity, convenience and intuitive results, and patients will not wait too long for examination results.

　　If intradermal test or prick test is an indirect method to determine specific IgE in vivo, then blood test is a means to directly determine specific IgE in serum.

　　Shi Haiyun, chief physician of the Department of Allergy, Beijing Shijitan Hospital affiliated to Capital Medical University, said that if patients are unable or unwilling to adopt intradermal test or prick test for various reasons, they can choose to directly determine the specific IgE in serum. If specific IgE can be detected and reaches a certain value, it can be preliminarily judged to be allergic. By measuring the content of specific IgE in the body, such as serum, the degree of allergy can be preliminarily judged. However, serum examination requires special equipment and high cost, and the patient needs to wait for several days or more for the examination results. In addition, at present, the types of allergens that can be detected by serum testing are limited.

　　If contact allergens are detected, patch test can be used, and when allergens are unknown, patch test can also be done. The operation method of patch test is to stick the reagent on the skin, and after observing for a period of time, judge whether the subject is allergic to the substance according to the skin’s reaction to the contact substance.

　　Liu Yongsheng added that another way to check allergens is provocation test, such as oral food provocation test, nasal mucosa provocation test, conjunctival provocation test and bronchial provocation test. The principle of these tests is to simulate a real allergic reaction, which has certain risks and is not often used in clinic.

　　Shi Haiyun said that allergen detection methods have their own advantages and disadvantages, and which allergen detection method to adopt should follow the doctor’s advice.

　　Liu Yongsheng said that after the allergen test, the doctor should make a comprehensive judgment according to the patient’s medical history to determine whether he is allergic. "In addition, patients should pay attention to observing and recording substances that may cause allergies in order to find and avoid corresponding allergens."

　　Allergen detection may have some blind spots.

　　Although the methods and techniques of allergen detection are relatively complete now, there are also cases in which allergens cannot be detected or allergens are misjudged in clinic. In this regard, Liu Yongsheng explained that due to many factors, to some extent, there are some blind spots in allergen testing.

　　Some blind spots are related to allergen detection methods. Taking the prick test as an example, patients with skin scratches may have false positive results. That is to say, some people were not allergic originally, and the allergen itself did not cause allergic reaction in patients, but acupuncture operation caused skin redness, swelling, itching and other reactions, which made inspectors mistakenly think that patients had allergic reaction.

　　Some blind spots are caused by external factors. For example, heating is one of the commonly used ways in food processing, and when food allergens are detected by immunological methods, heating will lead to changes in the structure of protein (allergen), so that antibodies cannot correctly identify the detected allergens, resulting in false negative results. For another example, ELISA is one of the commonly used methods to detect allergen wheat, but it is easy to cause false negative or false positive results because the samples are easily cross-contaminated.

　　Liu Yongsheng introduced that some blind spots of allergen detection are related to the complexity of allergen itself. There are about five or six hundred kinds of external allergens, and traditional methods can only screen 10 to 30 items, which is not comprehensive. Moreover, allergen detection is a meticulous work. For example, milk is one of the eight major allergic foods, and there are more than 30 kinds of allergic protein in milk. To determine which protein is allergic, more sophisticated detection means are needed. "Some people are allergic to cats, but whether they are allergic to cat hair, cat dander, cat saliva or cat urine, it is not clear from an allergen test." Liu Yongsheng said.

　　It is worth noting that some allergic patients take anti-allergic drugs before testing allergens, which will also cause false negative test results. Experts suggest that if the intradermal test is chosen to detect allergens, patients should stop taking antiallergic drugs for about 7 days, and some drugs need to stop taking them for a longer time.

　　"In addition, the relevant technologies and equipment for allergen testing and the level of doctors who test allergens for patients may also affect the results of allergen testing." Liu Yongsheng added.

　　"In order to accurately lock allergens, not only excellent technical means are needed, but also doctors need to patiently ask about medical history. Combining allergen detection methods and medical history to judge allergens, generally speaking, the results are relatively reliable. " Liu Yongsheng suggested that allergic people don’t need to do allergen testing regularly, but only when they have allergic symptoms but are not sure about allergens. In addition, they should choose professional and qualified institutions for testing.