The difference between IgE and IgG in food allergy testing

IgE targets immediate food allergy and is the globally recognized core basis for allergy diagnosis.； While IgG mostly points to food-related delayed immune reactions, its diagnostic value is currently controversial in the industry and cannot be directly used as a criterion for determining food allergy.

Speaking of which, I just encountered a typical example in the clinic last week. A young mother brought her 5-year-old baby to the clinic. She said that her mouth was red, swollen and had a rash after eating mango for half an hour. The IgE test confirmed that the mango was positive. Originally, she was diagnosed with food avoidance. However, she took a 100-item food IgG test at a physical examination institution. Eggs, milk, and soybeans were all 3 plus signs. She was so scared that she stopped all of them. In less than two months, the baby lost two pounds, often cried out that he was hungry, and his growth curve dropped. This is a typical example of confusing the meaning of the two tests, and you suffer in vain.

Let’s talk about the more familiar IgE first. It is like an acute alarm that explodes when touched. It mediates type I hypersensitivity reactions. After you come into contact with an allergenic food, it will quickly trigger mast cells to release inflammatory mediators such as histamine. Symptoms will appear in a few minutes or no more than 2 hours: mild rash, skin itching, sneezing, severe laryngeal edema, difficulty breathing, and anaphylactic shock. The risk is extremely high. The current guidelines of the World Allergy Organization (WAO) and the Allergy Branch of the Chinese Medical Association clearly regard serum specific IgE testing and skin prick testing combined with medical history as the core diagnostic criteria for immediate food allergy. The sensitivity and specificity have been clinically verified for many years. As long as the diagnosis is positive, you need to strictly avoid the corresponding foods, and there is no room for negotiation.

Let’s talk about the highly controversial IgG test. Many institutions now package it as “chronic food allergy testing” and “food intolerance testing”. In fact, the differences within the industry are very obvious. Most of those who support it are practitioners in the field of gastroenterology and functional medicine. They believe that IgG reflects the immune accumulation of the body after long-term exposure to certain foods. For problems such as chronic abdominal distension and diarrhea, recurring refractory eczema, and long-term unexplained fatigue for which no clear trigger can be found, the IgG results can be used as a reference for dietary adjustment. Indeed, many patients in clinical practice have significantly alleviated their symptoms after adjusting their diet based on the IgG results.

However, the attitude of the mainstream allergology community is also very clear: WAO and domestic allergy-related consensus have repeatedly emphasized that food IgG positivity can also occur in healthy people. This is essentially a manifestation of the body's normal immune tolerance to food. It does not mean allergy, nor does it need to be avoided. I took a food IgG test while doing a scientific research project last year, and the wheat antibody showed 2 plus signs. However, as a northerner, I never had any problems eating noodles and steamed buns. If I really followed the test results, I would lose half the fun of life.

As for ordinary people, they don’t have to worry about which one to choose. They can just decide according to their own symptoms. If an obvious allergic reaction occurs within a few hours of eating something, don't hesitate to check the IgE directly. The diagnosis can be confirmed based on the medical history, and it will be safe to strictly avoid food after that. If you have been suffering from chronic discomfort for a long time with no known cause, and have checked other problems without results, you can also check for IgG. However, do not cut off all food immediately if you get a positive result. It is best to find a doctor to make a judgment based on your daily dietary reaction - for example, if you eat eggs every day and don't feel any discomfort after eating, there is no need to stop even if the IgG shows 3 plus signs. Blind taboos will lead to malnutrition, which will have a greater impact on children.

Oh, by the way, many physical examination packages now like to promote dozens or hundreds of food IgG tests as high-end items, often costing thousands of dollars. If you don’t have long-term unexplained chronic discomfort, there is really no need to spend this wasted money. Finding out a lot of positives will only add psychological burden to yourself.

In the final analysis, whether it is IgE or IgG testing, they are just tools to assist diagnosis. The final determination must always be based on actual symptoms and medical history. When in doubt, it is much more reliable to consult an allergist at a regular hospital than to ponder on the test sheet yourself.