food allergy diagnosis

No single test can directly diagnose food allergy. The gold standard is the double-blind placebo-controlled food challenge test. The diagnosis must be made based on a combination of attack history, auxiliary screening, and challenge tests, so that the accuracy can reach more than 95%.

When I went out to the clinic last week, I met a mother who was holding a half-foot-thick test sheet. She said that her child had just turned 1 year old. The allergen screening done at the physical examination institution was IgE3+ for milk. The institution directly said that the child would never touch dairy products in his life. She even stopped breastfeeding. As a result, the child had not gained any weight in the past two months, and she was so anxious that she shed tears. This situation is so common. Many people think that if they take an allergen test report and see which item is marked with a plus sign, they are allergic to something. In fact, there are many ways to do this.

Nowadays, the two most common types of screening are skin prick tests and serum-specific IgE tests. They essentially check your body's allergy status to certain foods, but sensitization does not mean allergy. Nowadays, many primary medical institutions will directly make diagnoses based on the positive results of these two tests. However, in fact, the conventional positive predictive value of these two tests is only about 50%. To put it bluntly, out of 100 positive people, 50 are actually not allergic at all. There is also a controversy that has been going on for almost ten years: some doctors who practice functional medicine believe that elevated food-specific IgG can indicate chronic food allergy. According to the test results, dietary restrictions can improve long-term symptoms such as eczema and chronic diarrhea. ； However, the mainstream allergist community generally believes that elevated IgG is just a sign of immune memory. It only means that you have eaten this food and has nothing to do with allergies. Directly relying on the IgG results to avoid a wide range of foods can easily lead to trace element deficiencies and delayed growth and development. The mother I just mentioned misbelieved the IgG results and did not even dare to add ordinary complementary foods to her children.

We had treated a 5-year-old boy before. His mother had an IgG report of 3+ eggs, so he was given a ban for two years. He didn’t even dare to touch cakes. He was 2 centimeters shorter than his peers when he arrived. We gave him a provocation test. We beat hard-boiled eggs into powder and mixed them into rice cereal, starting from 1g. He ate the whole egg without even a rash. The mother cried at that time, saying that she had treated her child badly in the past two years. Do you think he was wronged?

Speaking of which, we have to mention our industry-recognized gold standard double-blind placebo-controlled food challenge test. To put it bluntly, the food suspected of allergy and the placebo are made into identical capsules or pastes. Doctors and patients do not know what they are eating. They start with a small dose and gradually increase the amount. Continuous observation for 4-6 hours. If no allergic symptoms appear, it means that you are not allergic. If there are any, it will be confirmed. This accuracy rate can reach more than 98%. However, this test is not a panacea. Firstly, it is time-consuming, and it only takes half a day to do it. Secondly, it has the risk of inducing severe allergic reactions. Therefore, it is generally only recommended when there is a high degree of suspicion, but other tests and medical history are not consistent. If the medical history is really clear, there is no need to suffer this sin.

Oh, by the way, in fact, many clinicians value your own food diary more than going through various examinations. When I meet a patient who is unsure, I usually ask him to keep a food diary for two weeks. What he ate at each meal, how much he ate, and whether he had any symptoms such as rash, itching, vomiting, wheezing, or diarrhea within 24 hours after eating. In many cases, after reading the diary, the allergen can be basically identified, and there is no need to even do an examination. For example, there was a college student who had redness, swelling and itching around his mouth within half an hour of eating mangoes. The sIgE test was negative. I directly told him that he was allergic to mangoes and just don’t touch them in the future. This typical rapid symptom is more accurate than any test report.

Having been in this business for almost ten years, my biggest feeling is that food allergy diagnosis is really not as simple as everyone thinks, nor is it a one-time deal. Some people were allergic to milk when they were young, and got better after puberty. Some people were fine eating shrimp before, but suddenly they went to the emergency room after eating shrimp. Immunity is too flexible. How can a test report be enough to say it's fatal? If you really suspect that you are allergic, don't randomly check those unreliable tests, and don't blindly limit your diet. It's better to go to the allergy department of a regular hospital.