The symptoms of food allergy are diverse and occur in a variety of organs, including the oral cavity (oral allergy syndrome), skin (urticaria and acute atopic eczema), inhalation system (rhinitis and asthma), gastrointestinal system (nausea, vomiting, abdominal pain and diarrhea), and other symptoms (e.g., conjunctivitis, angioedema, systemic allergic reactions, etc.). It is now generally accepted that whole food allergenic proteins not only act on the gastrointestinal mucosa but may also be absorbed systemically as bioactive substances.
We consume a wide variety of foods on a daily basis, which makes the diagnostic procedure of food allergy more complex.
Depending on the effector organ and its symptomatic manifestations, many inflammatory and other disease conditions must be ruled out before a diagnosis of food allergy can be confirmed. It may be helpful to determine whether a food allergy is present if the medical history suggests that the patient’s symptoms are related to food or beverage intake, although, of course, food allergy is only a subcategory of adverse food reactions.
It is very important to rule out food poisoning or infectious disease.
That is, if two or more people are exposed to the same food and both react, it is likely that the reaction is triggered by a mechanism other than allergy. Similar allergic symptoms may also be part of foodborne poisoning. Another differential diagnosis includes inherited or acquired metabolic defects, of which lactase deficiency is probably the most common, and alcohol intolerance in adult and adolescent patients, where alcohol can also be a cofactor in triggering food allergy by lowering the threshold dose at which patients can produce a reaction.
Taste can also mediate physiological and pathological responses and trigger certain conditioned manifestations, such as aversion. In this case, the taste receptors are stimulated to elicit a central nervous reflex that eventually leads to a reaction that can be mistaken for a food allergy. This, together with the underlying psychological fear caused by a severe reaction triggered by the previous ingestion of a certain food, is the main reason for the use of double-blind placebo-controlled provocation tests in the diagnosis of food allergy. After considering and ruling out the differential diagnosis mentioned above, the diagnosis of food allergy can be made if the amount of food that triggered the patient’s reaction can be tolerated by the majority of individuals in the population.
Positive provocation with allergic foods can strongly support this diagnosis, but positive provocation by itself does not indicate the mechanism of the disease.
By definition, food allergy is a food hypersensitivity reaction with immunologic properties, whereas non-immunologic food hypersensitivity reactions (described earlier as food intolerance) depend on other mechanisms that may not yet be clear. Since the latter disease condition is not exhaustively described in terms of pathophysiology, it is important to establish a clinically validated diagnostic method for food hypersensitivity reactions that does not rely solely on laboratory or other clinical ancillary tests.
The results of specific skin tests for food allergy are for informational purposes only and do not necessarily have diagnostic value. Negative skin test results have no exclusionary diagnostic value due to.
1. non-IgE-mediated skin tests can be negative.
2, allergen preparations prepared with raw materials, and food after cooking, digestion allergenicity may have changed.
3, certain fruits and vegetables of commercial preparations of allergen components are unstable, and the potency is greatly reduced after a period of storage, freshly squeezed juice can be used instead of prick test to improve the sensitivity of detection, but a positive control (histamine) should be established, except for false positive reactions caused by physical and chemical stimuli. For patients with severe allergic reactions, intradermal testing is dangerous and should be used with caution, and in vitro testing or prick testing is recommended instead.
The diagnosis of food allergy requires a reliable link between the patient’s medical history and the immunological principles of food allergy, and the patient may have had an adverse reaction to one or more foods. The first step in the evaluation of a patient with an adverse food reaction is to obtain a detailed medical history. This history is not sufficient as the sole criterion for the diagnosis of food allergy, but it can provide the clinician with a basis for assessing the severity of the allergic reaction. The most common symptom of food allergy is oral contact urticaria (i.e., swelling and itching of the oral mucosa immediately after contact with an allergic food), a mild reaction. Systemic reactions, on the other hand, may involve one or more target organs, including the skin, gastrointestinal tract, whistling tract, and cardiovascular system. Anaphylactic reaction is the most severe clinical manifestation of food allergy and requires medical emergency. It is defined as a systemic and potentially fatal allergic reaction.
The next second step is to establish a link with IgE-mediated pathophysiological clinical reactions by in vitro or skin prick tests for specific IgE testing of suspected foods. However, these diagnostic tests can only indicate the presence of food-specific IgE antibodies and cannot be used to confirm the diagnosis of food allergy. To demonstrate a clinical association between reported medical history and detected food-specific IgE, a final verification with a positive food provocation test is often required. If the diagnostic criteria are adequately met, clinicians should try to avoid the use of food excitation verification tests in cases of anaphylactic reactions.
The quality of the diagnostic test depends not only on the extract, but also on the pathogenesis of the food allergy.
In infants and children, food allergy mostly results from primary sensitization of the gastrointestinal tract to a food allergen that is digestive resistant. A striking feature of food allergy in adults is the high incidence of secondary food allergy, where the primary sensitization process is caused by an inhaled allergen (i.e., pollen). This is due to the high structural homology of food allergens and inhalant allergens, which are recognized by the specific IgE of inhalant allergens based on cross-reactivity. Usually, diagnostic tests based on food extracts are more sensitive for primary food allergic reactions compared to cross-reactivity. It has been observed in primary food allergic reactions that for some foods, the higher the level of allergen-specific IgE, the higher the likelihood of an allergic reaction after excitation (the so-called 95% positive predictive value). However, this diagnostic step is not precise, most notably because it does not predict the severity of the food allergic reaction.
The evaluation of a patient with food allergy also includes factors that may influence the severity of the allergic reaction.
Factors that may enhance food allergic reactions are physical activity, as well as NSAIDs, beta-blockers, and alcohol intake. Another important factor influencing allergic reactions is the dose or intake of allergic foods. The use of double-blind, placebo-controlled food provocation trials can provide important information about the effect of dose on the development of allergic symptoms in the individual patient being tested. Very low doses of food do not trigger allergic symptoms, indicating the presence of a no observed adverse effect dose (NOAEL), i.e., a certain amount of allergenic food is safe for the individual patient. As the dose increases, patients often experience mild symptoms of food allergy first, with more severe systemic symptoms often occurring at higher dose exposures.
There was a 7-year project on food allergy-specific immunotherapy aimed at establishing a safe and effective treatment for food allergy.
Based on the prevalence and importance of fish and fruit in a healthy diet, the project focused on the treatment of persistent and severe allergic reactions triggered by these two foods. The use of subcutaneously injected food extracts for the treatment of food allergies has been shown to be effective, but also very dangerous due to the possibility of triggering some allergic side effects.The aim of FAST is to develop a safe alternative by replacing the aqueous food extract solution with a hypoallergenic recombinant allergenic original as the active ingredient. In addition, hypoallergenic allergens need to be adsorbed on aluminum hydroxide in order to improve safety. The first part of the FAST project was to evaluate several methods to obtain hypoallergenic allergens.
It is also important to assess the safety and potential allergenicity of genetically modified foods.
Knowing which food proteins bind to IgE is critical information. If derived from a known allergen source or homologous to a known or recognized allergen in a database, serum screening of GM protein products using sera from subjects sensitive to the allergen source or homologous allergen is required. With the advent of molecular metaplasmology, the understanding of IgE binding proteins and their IgE antibody properties continues to improve. The importance of molecular metaplasmology for the evaluation of transgenic foods is immeasurable. It is now becoming increasingly feasible to establish the relevance of IgE antibodies to transgenic proteins. On the other hand, the ability of a protein to increase the induction of IgE production, i.e., the potential for sensitization, cannot be scientifically predicted.
Food allergy is a very common and important group of allergic diseases.
The pathogenesis is mainly IgE-mediated type I allergic reactions. Rapid clinical manifestations are common and can involve multiple organs or systems at the same time, and in severe cases, anaphylaxis may cause death. The diagnosis should be made based on a comprehensive analysis of the medical history, skin tests, and specific IgE test results. The double-blind placebo-controlled food provocation test (DBPCFC) is currently recognized as the gold standard for the diagnosis of food allergic reactions. The best treatment at this stage is still abstinence from allergenic food products and prompt symptomatic management in case of accidental exposure induced symptoms. In the future, there may be new testing methods and treatments such as allergen fraction, anti-IgE, and specific immunotherapy, which need to be further verified and studied.