Food allergen IgE

Food allergen IgE, the full name of food-specific immunoglobulin E, is the core immune marker that mediates immediate food allergic reactions. Simply put, if you are allergic to a certain food and it is of the IgE-mediated type, there will be IgE antibodies corresponding to the food in your body. Once the food is ingested, it may trigger symptoms such as rash, laryngeal edema, vomiting and even anaphylactic shock in as little as a few minutes. This is currently the most commonly used detection indicator for clinical diagnosis of food allergy.

Last month, I was in the allergology department when I saw a mother rushing in with her 3-year-old baby. She was holding a stack of test reports in her hand. She said that she had tested food IgE at a physical examination institution and found that mango, pineapple, and shrimp were all positive. For the past six months, she had not dared to feed her baby anything. Recently, her baby was half a head shorter than her peers, and she was extremely anxious. I first asked, "Have you ever eaten these things before?" What's your reaction? ”Bao's mother was stunned for a long time and said that her mouth was red after eating a mango once, but she had never dared to eat other fruits.

In fact, this is also the biggest point of disagreement about food IgE testing in clinical practice. One school of thought believes that as long as the specific IgE (sIgE) value exceeds the reference threshold, it means that sensitization has occurred. Regardless of whether there are symptoms or not, it must be strictly avoided to avoid inducing severe allergies.； However, another group of doctors who prefer evidence-based medicine believes that simple sIgE positivity can only mean that there are corresponding antibodies in the body. 30% to 40% of people are "asymptomatic sensitizers" and will not develop allergies at all. Blind taboos can easily lead to malnutrition, especially in developing children. Both statements are supported by data, and there is no absolute right or wrong. The final judgment must be based on the actual situation of the patient.

There are two main types of food IgE tests available to everyone now. One is the skin prick test, which involves dropping various food extracts on the inside of the forearm and gently pricking the surface skin with a special small needle. After 15 minutes, you can see the size of the wheal. It is cheap and the results are quick, but it is greatly affected by the condition of the skin. For example, the skin of children with atopic dermatitis is inherently sensitive and it is easy to get false positives. The other is blood test for serum sIgE, which is relatively stable, but there is also the possibility of false positives. For example, some people have high total IgE, or have other immune system diseases or parasitic infections, which can also lead to high values ​​and cannot be directly equated with food allergies.

I once met a girl in her 20s who bought a food IgE testing package online to treat acne. She spent a few hundred dollars to test more than 100 foods, and the results were positive for wheat, eggs, milk, and soybeans. She followed her diet for half a year and didn't even dare to touch bread. She lost almost 20 pounds and her aunt put it off. As a result, she came to us for a provocation test. She ate steamed buns, boiled eggs, and drank milk. Nothing happened after 3 hours of observation. She was starved for more than half a year. To be honest, there are many home testing kits and IgE tests in some medical examination institutions. The threshold is set very low. A little antibody will report positive. The reference value is really limited. If you really want to be tested, it is recommended to go to the allergy department of a regular hospital.

When I receive a doctor myself, I never make a conclusion just by looking at the IgE value. I must first ask about the medical history - have you ever eaten this food? How long does it take for reactions to occur after eating? What was the response like? If you really get rash, wheezing, and vomiting every time you eat, then you should avoid it even if the number is not high. ； If you have never eaten it, or have had nothing to do with it, even if the value is higher, there is no need to avoid it directly. At most, you can just pay more attention when you eat a large amount for the first time.

By the way, there is another point that many people don’t know. Only about 60% of food allergies are IgE-mediated, and the rest are non-IgE-mediated. For example, many children have diarrhea and bloody stools after eating milk powder, and all IgE tests are negative. This requires parents to keep food diaries and combine it with endoscopy to confirm the diagnosis. Don’t think that normal IgE means they are definitely not allergic.

In the final analysis, food allergen IgE is a reference tool, not a "taboo verdict". If you are really not sure whether you can eat it, the most reliable thing is to do an oral food challenge test under the supervision of a doctor. Don't blindly follow the report of food allergens. In the end, if the allergy is not prevented, the body will be destroyed first, and the gain will not be worth the loss.