Recommendations for Preventing, Diagnosing and Treating Food Allergy in Children

Hives and/or angioedema are the most frequent signs. Hives (urticaria) usually appear suddenly, together with intense itching, mainly affecting the skin that has been in contact with the food (face, mouth, and hands). Oedema and swelling of soft tissues (angioedema) may also occur, with glottic oedema being the most dangerous, as it compromises the respiratory tract.

Acute gastrointestinal symptoms: nausea, vomiting, abdominal pain, or sudden-onset diarrhoea after eating the food. Generally in infants, rare in older children. Special mention should be made of the Food Protein-Induced Enterocolitis Syndrome (FPIES) or food-induced enterocolitis, which is a non-IgE mediated allergy.

Oral allergy syndrome: Oral or oropharyngeal pruritus after eating certain foods, usually fresh fruits and vegetables. This syndrome occurs very frequently in patients with allergies to pollen (grasses) and sometimes precedes a more serious condition: anaphylaxis. It can be prevented if vegetables are cooked.

Atopic dermatitis: Dryness, erythema, and skin irritation. In atopic dermatitis, it is common to find lgE-mediated hypersensitivity to various foods and inhalants, although the severity of dermatitis is not associated with food. It is necessary to establish the true clinical meaning of these lesions via elimination diet and the subsequent controlled provocation.

Bronchial asthma: Dyspnoea during bronchoconstriction and hissing respiration during auscultation. In highly food-allergic patients, asthma or pharyngo-conjunctival symptoms (conjunctivitis, rhinitis) may occur after inhalation of volatile food products that are more intensely released during handling or cooking.

Anaphylaxis: Up to 1% of patients sensitised to food may present with anaphylaxis. This is a very serious allergic reaction: it should be suspected when there is skin impairment immediately after the ingestion of a food (hives, angioedema). Associated clinical features in other systems: respiratory system (asthma, uvular oedema), digestive system (diarrhoea, vomiting). Sometimes several systems can be affected and lead to shock, so it is necessary to be familiar with anaphylaxis to treat it before it escalates to shock.

Skin tests (Prick tests):consist of exposing patients to the suspected allergen through a micro-puncture made with a lancet in the skin, usually in the forearm. They are safe and specific, with an elevated negative predictive value (NPV). The size of a positive reaction gives us some idea of the patient’s degree of sensitivity to a specific allergen; however, this varies greatly from patient to patient. In addition, extracts can be made for testing for a large group of allergens, which is very useful if we want to test for an atypical allergen. The preparation of diagnostic food extracts complicates the diagnosis. Purified allergens are better than recombinants, which are obtained by recombining nucleic acids in vitro. However, the latter are replicable and can be easily standardised.

With fruits and vegetables, the prick by prick test is preferable, bearing in mind that the peel is more allergenic than the pulp, and that there are different levels of allergenicity between varieties of the same species. If the reaction was anaphylactic, it is better to avoid the tests and measure the specific IgE instead.Intradermal reaction tests are not used in food allergy testing because they have not been shown to have diagnostic value and because they are also dangerous, as they may trigger a systemic reaction (Sicherer & Teuber, 2004). Patch testing, useful for assessing the cause of contact dermatitis, is also not commonly used in the diagnosis of food allergy.

IgE quantification: There is a correlation between the severity of clinical features and the presence of specific IgE against a wide variety of foods. These “in vitro” tests do not pose a risk of allergic reaction, are not affected by the medication the patient may be taking (antihistamines), and do not depend on the characteristics of the skin. This is very useful in paediatrics, especially in infants under 12 months of age, where sensitisation is not clearly reflected on the skin using the prick test. Specific IgE should not be confused with the measurement of total IgE. Patients with any type of allergic condition usually have very high levels of IgE in comparison to the rest of the healthy population. Although an elevated total IgE rate indicates that the patient may be atopic, this rate does not provide information about the patient's condition or which allergens the patient is sensitive to. The usefulness of this measure is limited, except for the diagnosis and follow-up of some diseases, such as parasite infections, broncho-pulmonary aspergillosis, hyperimmunoglobulin E syndrome, etc.)

Food-specific IgE is measured in levels of kU/L. Even if the test is positive, the patient may not be allergic (average levels may be found in food-tolerant patients). This is why clinical records are essential. However, these tests have a high positive predictive value in children (Sampson & Ho, 1997.

Molecular diagnostics (component-resolved diagnostics): Advances in recombinant protein research have made it possible to identify different types of IgE that bind to different epitopes or proteins in the same food. Molecular diagnostics are a set of highly sensitive and specific techniques that allow us to identify different types of IgE against different molecules of a single food (while distinguishing the potentially anaphylactic ones). These techniques also allow us to establish a prognosis of allergic symptoms. For instance, a patient may be hypersensitive to hazelnut and have different types of IgE. If the patient has a positive response to IgE Cor1, the patient will have very mild oropharyngeal symptoms or will even be tolerant to hazelnut. However, if the patient tests positive for IgE Cor 8, the symptoms are likely to be more severe and the patient may become anaphylactic because this protein is a lipid transfer protein (LTP) (De Knop et al., 2011) (Hansen et al., 2009).

While molecular diagnostics techniques for plant foods are very advanced, much remains to be done in the field of allergies to animal foods. This is the most specific type of testing and is highly sensitive, so the results obtained must be assessed by an expert.

Elimination diets: of various types. Elimination diets of the suspected food: improvement of the symptoms is observed at 2 weeks if the allergy is IgE mediated. In non-IgE mediated allergies, improvement can be observed after several weeks of exclusion (Lozinsky et al., 2015) . This type of diet is practised in paediatrics, especially when milk allergy is suspected, as shown below. Empiric elimination diet: The most potentially allergenic foods are removed from the diet and then introduced one by one. This diet is mainly used in chronic conditions (eosinophilic oesophagitis, chronic idiopathic hives, etc.). This type of diet should only be prescribed by a professional and should be monitored by a nutritionist, especially in children, as the exclusion of certain foods could affect their growth. Elemental diet: food is replaced by extensively hydrolysed amino acid formulas. It is used in very severe cases of food allergy.

Food-controlled provocation tests are highly diagnostic techniques (gold standard), but they involve risks. They should not be performed in case of anaphylaxis or severe systemic reaction, or in case the clinical record is highly suggestive, repeated, recent, and consistent with a previous allergological analysis.

Testing techniques that have not been shown to be useful in the diagnosis of food allergy: The determination of specific IgG, IgA, and IgM is of no use. Cytotoxic testing techniques (ALCAT) are not replicable and are not supported by the scientific literature. Other testing techniques, such as kinesiology, neutralisation, and electrothermal pulse have no value.

Specific oral immunotherapy (OIT) treatments are based on introducing the food orally at very small doses tolerated by the patient, while the doses are progressively increased. Thus, tolerance can be achieved while the amount of specific IgE decreases. These protocols last approximately 3-6 months, but may last longer if the patient is very allergic. These guidelines have been shown to be very effective for the treatment of milk and egg allergies.

Conventional immunotherapy. Immunotherapy has been successfully tested in some types of allergy to plant foods and has yielded good results in the treatment of eosinophilic oesophagitis (Armentia et al., 2018).