**4. Diagnosis of food allergy in AD**

The diagnosis of food allergy should be made following the discrimination of IgE- and non-IgE-mediated allergies. Diagnostic protocols for IFA have been proposed by various researchers, institutes and academic societies; however, the concept of dosage

Food Allergy in Atopic Dermatitis 235

elevated without the elevation of blood eosinophil numbers in AD patients and even in normal subjects in recent studies conducted [24]. In this report, food additives were shown to provoke xerosis (dry skin) and resultant pruritus consistent with AD. Among patients suspected to have AD, over 30% showed pseudoallergies to food additives [25]. The signs and symptoms caused by food additives can interfere with the interpretation of OFC and with the therapeutic process. ECP is specifically elevated in patients who ingest artificial chemical food additives [24] and elevated ECP has been used as a marker of pseudoallergic reactions due to food additives, particularly when blood eosinophil

IFA is approached initially by tests for allergen-specific IgE. The skin prick test (SPT) has a high negative predictive value (approximately 95%) and is most informative when it is negative; the positive predictive value ranges between 30% and 50% [3]. Therefore, SPT is useful for excluding IFA, but a positive result may only be suggestive of IFA. Laboratory testing for food-specific IgEs also has a high negative predictive value, estimated to be 75%, but its positive predictive value is low, ranging from 20% to 60%. Recently, the diagnostic levels of food-specific IgEs have been determined. The presence of specific IgEs at or above these levels offers a positive predictive value of approximately 95% for IFA. Although skin prick tests and serum IgE measurements can confirm sensitisation, neither of these tests can on its own prove clinical allergy to a specific food with reliability or consistency. Moreover, IgE-based laboratory tests will only predict IFA; IgE-based tests are not useful for the

In spite of the extremely high specific IgE and strong SPT usually associated with HDM, HDM rarely induces anaphylactic reactions following exposure. In contrast, food-induced IgE-mediated allergies, including systemic urticaria and anaphylactic allergic reactions, can occur when a patient has high specific IgE levels or strong skin reactivity for a food

**Interpretation of polysensitisation from the results by the SPT or allergen-specific IgE**  Polysensitisation to multiple allergens as the result of allergen-specific IgE and skin prick tests, especially to multiple food allergens, may be embarrassing to the physician. Sensitisation of the skin caused by the skin prick test and the presence of specific IgE do not

In cases of skin sensitisation, patients often show similar reactions (itching, rash, or urticaria) to contact with allergen in the skin prick test. Therefore, patients should avoid allergens which are positive by the skin prick test. Sensitisation to specific allergens by allergen-specific IgE does not always provoke allergy. Based on the level of allergenspecific IgE, IgE-mediated allergy can be predicted, especially for food allergens. Therefore, physicians should just consider IgE-mediated food allergy if patients have high

The immunopathogenesis of eczematous allergic reactions to food that occurs in non-IgEmediated food allergy is similar to that of allergic contact dermatitis in that it is T lymphocytemediated and associated with food-specific T lymphocytes [3]. For these reasons, atopic patch

testing (APT) has been used to investigate food-induced eczema.

numbers are normal.

diagnosis of NFA in AD [18].

indicate the presence of allergy [2].

allergen.

food-specific IgE. **Allergy patch test** 

**Skin prick test and specific IgEs in IFA** 

quantitation, along with the measurement of clinical severity changes on the basis of discrimination of IgE- and non-IgE-mediated food allergy, has clearly become the most important point in successful immunotherapy [7]. Because both the diagnostic and the therapeutic protocols for IgE- and non-IgE-mediated food allergies differ greatly, the major points in these protocols should be revised.

The two most important points regarding diagnosis of food allergy in atopic dermatitis are as follows: 1) distinction should be made between IFA and NFA and 2) the treatment dosage must be calibrated and the clinical severity assessed for the purposes of therapy and follow-up [7].
