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Keywords:

  • allergy;
  • diagnosis;
  • immunoglobulin E;
  • recommendations;
  • testing

Abstract

  1. Top of page
  2. Abstract
  3. Actual prevalence of allergic disease
  4. Who should be tested?
  5. Practical allergy testing
  6. Allergy treatment
  7. Conclusion
  8. Key points
  9. References

Allergic disease has become a major burden in westernized societies because of a recent rise in its prevalence. Approximately one-third of children suffer from an allergic disease, with the prevalence varying from 15 to 20% for atopic dermatitis, 7 to 10% for asthma and 15 to 20% for allergic rhinitis and conjunctivitis. Despite the increase, it is important not to assume a diagnosis of allergy on the basis of symptoms alone, because allergic and nonallergic conditions may present with similar symptoms. An accurate allergy diagnosis is important in order to treat the patient most appropriately and to potentially prevent or delay the development of allergic disease. A good clinical history is the starting point for accurate allergy diagnosis but is not unequivocal. The European Academy of Allergy and Clinical Immunology has recognized the importance of allergy testing and therefore developed evidence-based recommendations on allergy testing in children. Widespread adherence to these recommendations should improve the quality of care for allergy patients. Cooperation between all healthcare professionals involved in the treatment of allergy patients is also a key to improve our response to the allergy epidemic.

The prevalence of allergic diseases has risen considerably in the last 20–30 years (1, 2), with the effect that allergic disease is now considered a major burden in westernized societies. Approximately one-third of children suffer from allergy of some nature, with varying prevalences depending on the diagnosis (Table 1) (2–4). Despite the increase, allergy should not be assumed to exist in patients on the basis of symptoms alone, because allergic and nonallergic conditions can present with similar symptoms. Indeed, it has been estimated that 60–70% of chronic ‘allergic’ disorders are the result of organ defects and factors other than allergy (5).

Table 1.  Allergic diseases in childhood
AgeDiagnosisPrevalence (%)IgE sensitization (%)
  1. Adapted from Host et al. (29), with permission from Blackwell Publishing.

Early childhoodFood allergy7–840–60
School ageFood allergy1–260–70
ChildhoodAtopic dermatitis15–2033–40
Early childhoodRecurrent wheeze/asthma21–3430–60
School ageAsthma7–1070–90
ChildhoodRhinitis and conjunctivitis10–1560–80

It is important to correctly identify allergy for a number of reasons. If symptoms in a patient are identified as being caused by allergy, then specific measures to control and treat these symptoms can be instigated. In the case of children, it is particularly important to identify those individuals at an early stage who are at increased risk for later development of allergic diseases. By doing so, it may be possible to put measures into practice to stop or delay the progression of allergic disease with age, a concept known as the ‘allergic march’. It is equally important to rule out allergy as a cause of symptoms. In this way, trials of various medications can be avoided and further diagnostic investigations initiated. In addition, ruling out allergy can avoid futile avoidance measures that may be upsetting a child (for example, having to remove a pet from the house), or potentially harmful (for example, adhering to a limited diet if food allergy is assumed on the basis of positive tests alone).

During infancy, the main symptoms of possible allergic nature are dermatitis, gastrointestinal effects and recurrent wheezing, whereas in older children, bronchial asthma, rhinitis and conjunctivitis are the main symptoms (6, 7). The proportions of patients with common allergic-like symptoms who have been reported to actually have an allergy are detailed below.

Actual prevalence of allergic disease

  1. Top of page
  2. Abstract
  3. Actual prevalence of allergic disease
  4. Who should be tested?
  5. Practical allergy testing
  6. Allergy treatment
  7. Conclusion
  8. Key points
  9. References

Asthma

Asthma that begins early in life is usually associated with atopy, and the prevalence of immunoglobulin E (IgE)-mediated wheeze and asthma tends to increase with age. However, as mentioned previously, not all early wheezing is because of allergy. Indeed, data suggest that only approximately one-third of young children with wheeze are allergic. For example, a UK study evaluating the development of allergic diseases in 4-year-old children suggests that only 29% of children with persistent wheeze are sensitive to at least one common aeroallergen (8). Similar results have been reported from Italy and Australia (9, 10). In older children, however, allergy is more commonly the cause of wheezing or asthma, with studies reporting the proportion of children with allergic asthma to be about two-thirds of those with symptoms (3, 8–16). For example, children with allergic, asthma-type symptoms may, in fact, be suffering from gastro-oesophageal reflux, sinusitis or vocal-cord dysfunction.

Rhinitis

The prevalence of nonallergic rhinitis in children has been reported to be 25–52% (17–19). Patients may have coexisting allergic and nonallergic disease; in a retrospective analysis of 975 patients attending an allergy clinic, 43% of patients had allergic rhinitis, 23% nonallergic rhinitis and 34% mixed rhinitis (20, 21). Importantly, 44% of the patients who had been diagnosed as having allergic rhinitis also had a nonallergic element (e.g. a reaction to viral/bacterial infection or chemicals, or an organ defect) to the disease, which would have required a different management strategy.

Eczema

The role of allergy in eczema has been assessed in a number of studies. In a UK birth cohort study involving 1456 children aged 4 years (5), the prevalence of an associated allergic disease or positive allergy tests in children with eczema was 43%, with house-dust mites, grass pollen and cats being the most common allergens to which children were sensitized. A German study comparing the prevalence of allergic eczema in 1273 preschool children in the former East and West Germany over a 7-year period (22, 23) showed similar results to the UK study. By comparison, the authors of hospital-based studies in Hungary and France estimated the proportion of patients with eczema-associated allergies to be 54 and 85%, respectively (24, 25). Despite variations between countries in the prevalence of allergy, it is clear from all these studies that allergic disease should not be assumed on the basis of symptoms alone. Foods play a role as an additional allergic trigger mainly in infants and young children, with various studies having shown that approximately one-third may suffer from food allergy (26–28).

Who should be tested?

  1. Top of page
  2. Abstract
  3. Actual prevalence of allergic disease
  4. Who should be tested?
  5. Practical allergy testing
  6. Allergy treatment
  7. Conclusion
  8. Key points
  9. References

Considering the recent rise in the prevalence of allergy, the difficulty in determining the nature of allergic-type symptoms and the importance of identifying allergy early in childhood, it is clear that sound, scientifically-based recommendations for allergy testing are needed in order to ensure high-quality, effective diagnosis and treatment of allergy. Such guidelines would also help to standardize practice, which is often quite different both between and within countries. In recognition of this need, evidence-based recommendations have been established by the Pediatrics section of the European Academy of Allergy and Clinical Immunology (EAACI) (7, 29). These state that, generally, all individuals with severe, persisting or recurrent possible ‘allergic symptoms’ and individuals with a need for continuous prophylactic treatment should be tested for specific allergy irrespective of the age of the child. Expanding on this, they suggest that the extent of allergy testing will typically depend on the age of the child, the family history and the character of the symptomatology, including possible seasonal or diurnal variations. The EAACI proposals for allergy testing and relevant allergens at different ages are given in Table 2.

Table 2.  Allergy testing according to age in individuals with atopic dermatitis (AD)
  1. Adapted from Host et al. (29), with permission from Blackwell Publishing.

<3–4 years of age
 Foods (for AD-associated food allergy)
  Cow's milk
  Egg white
  (peanut, wheat, nuts, fish, etc.)
 Inhalant allergens (to test the atopic risk)
  House-dust mites
  Cats, dogs and other furred animals
  Pollens
>3–4 years of age
 Foods (in case of severe persisting AD for AD-associated food allergy)
  Cow's milk
  Egg white
  Peanut
  (wheat, nuts, fish, etc.)
 Inhalant allergens (for allergen-associated AD)
  House-dust mites
  Cats, dogs and other furred animals
 Inhalant allergens (to test the atopic risk)
  House-dust mites
  Cats, dogs and other furred animals
  Pollens

Practical allergy testing

  1. Top of page
  2. Abstract
  3. Actual prevalence of allergic disease
  4. Who should be tested?
  5. Practical allergy testing
  6. Allergy treatment
  7. Conclusion
  8. Key points
  9. References

Allergy testing may include some or all of the following: taking a case history, determination of IgE sensitization, allergen challenges, other tests (e.g. the histamine release test and patch tests) and environmental investigations. The importance of a good clinical history cannot be overemphasized. Frequency and severity of symptoms, family history, environmental factors (e.g. at home, at school and during leisure time) and exposure to pets and tobacco smoke should all be investigated. In a study assessing the value of a rigorous clinical history in order to identify respiratory allergy, negative diagnoses made during the clinical history were confirmed in 77% of patients by a negative provocation test (30). Positive provocation tests occurred in 64% of patients with a positive clinical-history diagnosis. Despite this, a clinical history is not infallible: testing is therefore used to complement effective history-taking. The detection of IgE antibodies in blood and the performance of skin-prick, skin-patch and double-blind, placebo-controlled food challenge tests may be used for testing. The presence of raised total serum IgE (31) increases the chance of an individual being sensitized to allergens, but this method may give false-positive and -negative results for specific allergies. Frequently, children with individual allergies present with normal total serum IgE levels. Tests that measure specific allergies should be chosen on the basis of the physician's knowledge of the allergens that are statistically most likely to cause symptoms in different age groups (Table 2). Knowledge of seasonal allergens and how these differ regionally is also important. In circumstances in which it is difficult to obtain an accurate history — for example, in young infants — an IgE screening test may be particularly useful, which assesses specific IgE levels in response to a range of common allergens. If this test is positive, further specific testing can be used to identify the relevant allergen(s). Specific allergy treatment can then be initiated.

Allergy treatment

  1. Top of page
  2. Abstract
  3. Actual prevalence of allergic disease
  4. Who should be tested?
  5. Practical allergy testing
  6. Allergy treatment
  7. Conclusion
  8. Key points
  9. References

Once allergy testing has identified the presence of allergy or those individuals at an increased risk for the development of allergic disease in the future, effective treatment can be instituted. Specific allergen avoidance measures, relevant pharmacotherapy and specific allergy immunotherapy can all be initiated in order to treat the symptoms of disease and also, potentially, to slow or prevent the development of subsequent allergic disease. Avoiding allergen exposure is a logical way to treat allergic disease, but may not always be feasible. It is possible to reduce exposure to house-dust mite allergens through the use of fairly simple measures (32). It is less straightforward to reduce exposure to pet allergens, however. Even if pets are removed from the home, pet allergens are ubiquitous in the environment outside the house and therefore, avoidance is not easy.

Conclusion

  1. Top of page
  2. Abstract
  3. Actual prevalence of allergic disease
  4. Who should be tested?
  5. Practical allergy testing
  6. Allergy treatment
  7. Conclusion
  8. Key points
  9. References

Allergy testing is key to ensuring that patients receive the best possible care, whether this is through the implementation of measures to avoid subsequent allergy development or the use of specific allergy treatment to treat their symptoms. The EAACI recommendations provide valuable guidance regarding allergy testing and should therefore be largely implemented. The implementation of these guidelines, together with effective cooperation between primary-care physicians and allergists, should improve the effectiveness of the way we care for our patients in this time of rising allergy prevalence.

Key points

  1. Top of page
  2. Abstract
  3. Actual prevalence of allergic disease
  4. Who should be tested?
  5. Practical allergy testing
  6. Allergy treatment
  7. Conclusion
  8. Key points
  9. References
  • Symptoms often presumed to be allergy are, in approximately half of cases, not because of allergy.
  • Comprehensive allergy testing is important in children in order to predict or prevent the allergic march.

References

  1. Top of page
  2. Abstract
  3. Actual prevalence of allergic disease
  4. Who should be tested?
  5. Practical allergy testing
  6. Allergy treatment
  7. Conclusion
  8. Key points
  9. References
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