Allergy Survey ②
Combined with allergen detection methods and medical history to determine allergens, the results are generally more reliable.
People with allergies do not need to do allergen testing on a regular basis. They can do the testing when they have allergic symptoms but are not sure about the allergen. In addition, they should choose a professional and qualified institution for testing.
Liu Yongsheng
Director of Dermatology, Aviation General Hospital
Are allergen tests reliable?
This is one of the most frequently asked questions by Hu Liang, a pediatrician at Changchun Children's Hospital.
Many people suffer from allergies. In order to find allergens, they go to the hospital for allergen testing. The result is that "the test was lonely", and the test results do not seem to be of much help in controlling allergies.
So, what are the main methods of allergen testing?
How effective are these methods?
Why do some people feel that they are "tested for nothing"?
Around these issues, reporters from Science and Technology Daily interviewed relevant experts.
Identifying allergens is key to managing allergies
Allergic diseases are also known as allergic diseases, commonly known as allergies.
Data show that 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.
Allergies are closely related to allergens.
Jiang Weihong, chief physician of the Department of Otolaryngology and Head and Neck Surgery at Xiangya Hospital of Central South University, said that allergens enter the human body through oral, inhalation, contact or injection, bites and other routes and cause allergic reactions in the human body.
Therefore, in order to control allergies, the key is to diagnose and identify the allergen.
Only by identifying the cause of the allergy can the correct treatment plan be selected.
However, there are many types of allergens in life, the most common are ingestion allergens and inhalation allergens, and some are contact allergens.
So, how can we "pull" out the real allergens that cause allergies?
This requires allergen testing.
Liu Yongsheng, director of the Department of Dermatology of Aviation General Hospital, said that after exposure to allergens, patients with allergic constitution will produce corresponding specific IgE in the body, and then the specific IgE will enter the circulatory system and be transported to all parts of the body, where it is associated with hypertrophy in specific parts. Cells and basophils bind.
Mast cells and basophils that bind specific IgE will again encounter and bind to the allergen, which then triggers the release of inflammatory factors, such as histamine, from mast cells and basophils, which can directly lead to allergic reactions Inflammation, causing the human body to appear type I allergic reaction symptoms.
"So, in the so-called allergen test, the substance checked is specific IgE." Liu Yongsheng said.
Different detection methods have their own advantages and disadvantages
Liu Yongsheng introduced that the methods of checking allergens are roughly divided into intradermal test or prick test, serum test, patch test and challenge test.
The principle of intradermal test or prick test is to let a certain amount of allergen enter the skin through a specific way, and then observe whether the allergen will cause an allergic reaction, and judge the degree of allergy according to the degree of local skin allergic reaction, which is commonly known as "needling". "an examination.
Liu Yongsheng said that the advantages of this method are that it is simple and convenient, the results are more intuitive, and the time for patients to wait for the test results will not be too long.
If intradermal test or prick test is an indirect method to measure specific IgE in vivo, then blood test is a method to directly measure specific IgE in serum.
Shi Haiyun, chief physician of the Allergy Department of Beijing Shijitan Hospital affiliated to Capital Medical University, said that if patients are unable or unwilling to use intradermal tests or prick tests for various reasons, they can choose to directly measure specific IgE in serum.
If specific IgE can be detected and reach a certain value, it can be initially judged to be allergic.
By measuring the content of specific IgE in the body such as serum, the degree of allergy can also be preliminarily judged.
However, serum testing requires special equipment and costs, and patients need to wait several days or more for the test results.
In addition, the types of allergens that can be detected by serum testing are limited.
A patch test can be used to detect contact allergens, or when the allergen is unknown.
The operation method of the patch test is to stick the reagent on the skin, observe for a period of time, and judge whether the subject is allergic to the substance according to the skin's reaction to the contact object.
Liu Yongsheng added that another method for checking allergens is the challenge test, such as oral food challenge test, nasal mucosa challenge test, eye conjunctiva challenge test, bronchial challenge test, etc.
The principle of these tests is to simulate the process of a real allergic reaction, which has a certain risk and is generally not used in clinical practice.
Shi Haiyun said that allergen detection methods have their own advantages and disadvantages, and which allergen detection method to use should follow the doctor's advice.
Liu Yongsheng said that after the patient has been tested for allergens, the doctor should make a comprehensive judgment based on the patient's medical history to determine whether he is allergic.
"In addition, patients should pay attention to observe and record substances that may cause allergies in order to find and avoid corresponding allergens."
Allergen detection may have some blind spots
Although allergen detection methods and technologies are relatively complete today, there are still cases in which allergens cannot be detected or the allergens are wrongly judged in clinical practice.
In this regard, Liu Yongsheng explained that due to various factors, to a certain extent, there are some blind spots in allergen detection.
Some blind spots are related to allergen detection methods.
Taking the prick test as an example, patients with skin scratching may have false positive results.
That is to say, some people are not allergic at first, and the allergen itself did not cause allergic reaction in the patient's body, but the acupuncture operation caused skin redness, swelling, itching and other reactions, which made the inspectors mistakenly believe that the patient had an allergic reaction.
And some blind spots are caused by the interference of external factors.
For example, heating is one of the commonly used methods in food processing. When using immunological methods to detect food allergens, heating will cause changes in the structure of proteins (allergens), so that antibodies cannot correctly identify the detected allergens. produce false negative results.
For another example, ELISA method is one of the common methods for detecting allergen wheat, but because samples are easily cross-contaminated, it is easy to lead to false negative or false positive results.
Liu Yongsheng introduced that some blind spots in allergen detection are related to the complexity of the allergen itself.
There are about 500 or 600 kinds of external allergens, and traditional methods can only screen 10 to 30 items, which is not comprehensive.
Moreover, allergen detection is a delicate task. For example, milk is one of the eight major allergic foods, and there are more than 30 allergenic proteins in milk. To determine which protein is allergic, more sophisticated detection methods are required.
"Some people are allergic to cats, but whether they are allergic to cat hair, cat dander, or cat saliva and cat urine, this cannot be determined by a single allergen test." Liu Yongsheng said.
It is worth noting that some allergic patients take anti-allergy drugs before testing for allergens, which can also cause false-negative test results.
Experts suggest that if the method of intradermal test is selected to detect allergens, patients should stop taking antiallergic drugs for about 7 days, and some drugs need to be stopped for a longer time.
"In addition, related technologies and equipment for allergen testing, as well as the level of doctors who perform allergen testing on patients may also affect allergen testing results." Liu Yongsheng added.
"To accurately target allergens, we not only need excellent technical means, but also need the doctor to patiently ask about the medical history. In general, the results are relatively reliable by combining allergen detection methods and medical history to determine allergens." Liu Yongsheng suggested that people with allergies do not need to Do allergen testing regularly, wait until you have allergy symptoms but you are not sure about the allergen. In addition, you should choose a professional and qualified institution for testing.