1. Diagnosis, treatment and prevention of allergic disease: the basics

Jo A Douglass and Robyn E O’Hehir
Med J Aust 2006; 185 (4): 228-233. || doi: 10.5694/j.1326-5377.2006.tb00539.x
Published online: 21 August 2006
Making the diagnosis
Is it allergy?

Allergy can be defined as a detrimental immune-mediated hypersensitivity response to common environmental substances. While the word “allergy” can mean many things to the lay person, the clinician needs to keep in mind that diagnosis of allergies is critically dependent on identifying the immune processes involved in the allergic response.

The immune processes of allergy usually rely on the production of IgE antibodies specific to common allergens. Allergic diseases are caused by the activation of mast cells and basophils through cell-surface-bound IgE. This causes the release of histamine and other mediators, leading to allergic inflammation. Chronic allergic inflammation characteristically involves a cellular tissue infiltrate of eosinophils and lymphocytes associated with chronic tissue damage. This definition of allergy is intentionally restrictive and, for the purposes of this article, excludes cutaneous contact allergy, which is mediated by T cells rather than IgE.

In the community, diverse symptoms are often attributed to “allergy”. A useful test for the clinician is to ask whether the symptoms are, or could be, IgE-mediated (IgE-mediated symptoms include asthma, rhinitis, urticaria, eczema, food hypersensitivity and anaphylaxis). If not, then the symptoms are unlikely to be the result of true allergy.

IgE is produced by B lymphocytes directed by cytokine release from T helper (TH) lymphocytes (Box 1). In people with allergies, the TH lymphocytes secrete cytokines that stimulate the production of IgE antibodies to allergens. The condition of secreting IgE in response to common environmental allergens is called “atopy”. Predisposition to atopy is determined by both genetic and environmental influences, particularly in infancy, when immune responses to allergens are maturing, and T lymphocyte cytokine production is influenced by environmental exposures.

Allergic diseases include allergic rhinitis and asthma; food and stinging insect allergies leading to anaphylaxis; and allergic dermatitis. The diagnosis of allergic disease depends on identifying both the symptoms on allergen exposure and the relevant allergen-specific IgE. For example, an individual who develops rhinitis in early spring may be sensitive to grass pollen, and identifying IgE specific to rye grass pollen confirms the likely aetiology. However, identification of house dust mite-specific IgE in the same individual in the absence of rye grass pollen-specific IgE may suggest it is not an allergic process, as house dust mite is a perennial (year-round) allergen, and seasonal exacerbation of symptoms is unlikely to be related to exposure to this agent.

The manifestation of allergic diseases changes throughout life: food allergies and eczema are most likely to develop in infants, asthma in young children, and rhinitis in older children and adults (Box 2).1 There is increasing evidence that appropriate treatment of allergies can prevent and alter the natural history of allergic diseases. Optimal treatment requires accurate determination of allergic triggers. Moreover, if an allergen avoidance strategy is to be pursued in relation to food or aeroallergens, it is critical to minimise the inconvenience of this strategy by making a correct diagnosis as early as possible.

Detecting allergen-specific IgE

Accurate diagnosis of allergic disease and the relevant allergens helps to determine appropriate treatment options. Allergen-specific IgE can be detected by skin prick testing and by blood specific IgE testing (ie, serum allergen-specific IgE testing [as distinct from total IgE testing]).

Skin prick testing

Skin prick testing relies on the introduction of a very small amount of allergen extract into the epidermis using a standardised method to ensure reproducibility and comparability of results (Box 3). The results of skin prick testing are read at 10 minutes (for the positive control [histamine dihydrochloride or codeine]) and 15 minutes (for the allergen), and the diameter of the resulting weal is recorded in two dimensions. By convention, a positive test is one in which the mean of the two weal diameters is at least 3 mm greater than the negative control (saline), although if the reaction is as small as this, the relevance of the response is in question. Positive and negative controls are critical to enable interpretation of test results.2

When performed correctly, skin prick testing with aeroallergens (eg, house dust mite allergen, pollens, domestic pet allergens) shows good correlation with blood specific IgE testing in a semi-quantitative manner.3 However, careful patient selection for skin prick testing is critical for both safety and interpretation: absolute and relative contraindications to skin prick testing are listed in Box 4.

Although very rare, systemic reactions to skin prick testing, and even fatalities, have been reported, and therefore equipment and supplies for treating anaphylaxis (including oxygen and adrenaline) should be available at the testing site. Systemic reactions to skin prick testing are more common in infants or in cases where the reaction being investigated is systemic (as in true food allergies or allergies to latex or stinging insects). In these cases, skin prick tests should be performed with particular caution or avoided in favour of blood specific IgE testing.

Commercially prepared allergens for skin prick testing are usually standardised against either laboratory controls or by in vivo methods to ensure comparability between tests and reagents. Tests using mixes of foods or inhalant allergens are not recommended, as they can give results that are difficult to interpret. Where standardised reagents are not available, crude allergens can be used for testing, but the results require interpretation by an allergy specialist.

Intradermal allergy testing (in which a small amount of diluted allergen is injected into the dermis) has a very high non-specific reaction rate, but is useful in specific protocols for investigating drug and stinging insect allergy. Its use should be restricted to specialist clinics. Other methods of skin testing such as “scratch” testing are no longer used, owing to inconsistency of results.

Doctors wishing to conduct skin prick testing should refer to specific guidelines for conducting skin prick tests.2 Standardised conduct of testing is critical to identifying the relevant allergens, and interpretation of the results is equally critical. Where feasible, the requesting doctor should observe the patient’s skin prick tests to aid interpretation.

Management of allergic disease

Accurate diagnosis of the allergens responsible for allergic disease presents therapeutic opportunities for allergen-specific therapies such as allergen avoidance and immunotherapy (Box 5 and Box 6).

Allergen avoidance

Careful avoidance of the specific allergens responsible for allergic disease should always be the first consideration in managing patients with allergies. This is the primary form of treatment for food allergies and some stinging insect allergies, as avoidance can be a very effective strategy if patients are well educated about precautionary measures. For example, a person allergic to jumper-ant venom can minimise the chances of being stung by wearing shoes and long-sleeved shirts when outdoors and gloves when gardening. Accurate diagnosis of food allergies can enable patients to minimise the disruption to their lives caused by an unnecessarily restrictive diet.

However, allergen avoidance is particularly contentious when applied to the area of aeroallergens and respiratory allergic disease. People who are clearly allergic to animal allergens (eg, cat allergens) are generally not troubled by the allergy unless they encounter the animal, providing a strong case for allergen avoidance. Similarly, to give an example from the health care environment, avoidance of powdered latex gloves has been effective in reducing symptomatic latex allergy and the incidence of new cases in hospital staff.5 But the situation is less clear with respect to house dust mite allergen, the most common domestic allergen in Australia. While older trials of allergen avoidance suggested that it reduced asthma symptoms, bronchial reactivity and eczema, two recent studies in patients with asthma6 and rhinitis,7 confirmed by a meta-analysis,8 question these benefits and suggest that further studies of secondary treatment of asthma by allergen avoidance are unlikely to prove that the method is effective.

So, what should the treating doctor recommend? The evidence suggests that house dust mite avoidance should be recommended cautiously, if at all, and certainly only in people with clear sensitivity to house dust mite allergen. In symptomatic animal allergy, there is some evidence that removal from the home of a pet to which a person is allergic significantly reduces allergic symptoms and medication requirements.9 Although it is intuitively reasonable to reduce relevant allergen exposure in people with allergic symptoms, recent studies challenge the effectiveness of universal allergen avoidance strategies for allergies to domestic allergens.

Allergen immunotherapy

Allergen-specific immunotherapy involves administration of increasing doses of allergen to a patient to achieve clinical and immunological tolerance over time. Allergen injection immunotherapy induces T cell tolerance by several methods, including decreased allergen-induced proliferation, alteration of secreted cytokines, stimulation of apoptosis, and the production of T regulatory cells. This results in a reduction in inflammatory cells and mediators in the affected tissues, the production of blocking antibodies, and the suppression of IgE.10

The only absolute indication for immunotherapy is in patients who develop systemic reactions to insect venom, in whom incremental subcutaneous doses of venom can achieve tolerance to insect stings in 80%–90% of cases.11 However, immunotherapy for stinging insect sensitivity needs to be continued for at least 5 years to achieve durable tolerance.12 Conventional (subcutaneous) immunotherapy for allergic respiratory disease is clearly effective compared with placebo and requires 3 or more years of treatment to obtain durable efficacy.

Subcutaneous immunotherapy is very effective for seasonal allergic rhinitis caused by grass pollens. It has been shown in some studies to reduce symptoms by over 60%.13 While not first-line treatment for asthma, allergen immunotherapy has been shown to be effective in reducing airway responsiveness and exacerbation rates.14 Although the benefits of subcutaneous immunotherapy are apparent in both asthma and allergic rhinitis, the use of immunotherapy needs to be balanced against the inconvenience of its delivery and the risks associated with anaphylaxis due to allergen administration.

More recently, allergen immunotherapy for aeroallergens has been delivered by sublingual/swallow immunotherapy (SLIT). Meta-analysis of the many trials of this form of treatment confirms its safety and efficacy,15 but there are insufficient trials comparing sublingual immunotherapy with subcutaneous immunotherapy to compare similar dosing regimens. Moreover, efficacy with some allergens and in children is still under debate. However, if its efficacy for a broad range of allergens is proven, sublingual immunotherapy offers treatment that is probably more acceptable to patients and parents than subcutaneous immunotherapy. The major current drawback of sublingual immunotherapy is cost, as allergen doses required for effective treatment are at least 100-fold greater than those needed for subcutaneous immunotherapy. This translates into medication costs at least three times higher than for subcutaneous therapy. Poor patient adherence to prolonged courses of sublingual treatment may also be a factor reducing effectiveness.

There are also promising reports of sublingual immunotherapy for food allergies. While this approach needs to be further confirmed in extensive studies, and will need to be performed in specialist centres because of its high risk, this is a promising avenue of treatment for food allergy — an area in which current treatment relies on long-term avoidance for secondary prevention.16

Can allergy be prevented?
Primary prevention

“What can I do to prevent allergic diseases in my children?” This is a very common question asked by parents. Although there has been much conjecture on how to influence the infantile immune response to reduce the likelihood of allergen sensitisation and subsequent allergic disease, effective specific preventive therapies have not yet been developed. Nevertheless, the following recommendations all have some evidence of efficacy in preventing either allergen sensitisation or disease such as wheeze or eczema, or both, especially in children born to high-risk families.17

Maternal avoidance of certain foods during pregnancy and lactation has not been effective in preventing the onset of allergic disease, and cannot be recommended. As there is conflicting evidence for the effectiveness of avoidance of house dust mites or pets in infancy for preventing subsequent allergic sensitisation, no recommendations can be made at this time regarding these initiatives.

More relevant to primary prevention are large trials of multifactorial interventions, such as the Canadian Childhood Asthma Primary Prevention Study18 and the Australian Childhood Asthma Prevention Study.19 The Canadian study, which has now been going for 7 years, shows a significant odds ratio (0.39) for the prevention of current asthma in a cohort of high-risk children as a result of a multifaceted intervention that has included encouragement of breastfeeding and avoidance of house dust, pets and tobacco smoke. The results of other similar trials, and data demonstrating the durability of benefits, will be needed to formulate public health measures in this direction.

What’s on the horizon?

Researchers into allergen immunotherapy continue to seek safer and more convenient allergy “vaccines”.23 Peptide therapies based on the T lymphocyte epitopes of allergens offer hope in this area, but their clinical utility is yet to be demonstrated for all but cat allergy.24 Other approaches to allergic disease have been the development of humanised monoclonal anti-IgE antibodies, which have been found to have some efficacy in treating asthma25 and food allergies.26 Anti-IgE treatments may offer therapeutic opportunities for people with multiple sensitivities. Anti-cytokine therapies have also been investigated to treat asthma. Anti-interleukin-5 therapy has produced some reduction in inflammation, but has failed to improve bronchial hyper-responsiveness.27 Early trials of tumour necrosis factor alpha (TNF-α) blocking have shown some success, but further work is needed on specific blockers in inflammatory pathways.28

Future options for treating allergic disease will focus on allergen-specific routes, including further development of immunotherapy and targeting of specific mediators — an area with a great deal of promise, especially in people with refractory disease.

5 Case scenario*

A 24-year-old man presented complaining of food allergies involving many foods. He reported long-standing seasonal rhinitis, which had been a particular problem when he lived in Europe as a teenager, but had been less troublesome since his return to Australia 3 years previously.

He had been aware for many years of oral tingling and minor throat swelling on eating apricots, and generally avoided them. He had had no systemic or gastrointestinal symptoms on eating apricots, and had not experienced anaphylaxis after eating any foods. However, he had noticed more recently that bananas, raw apples, kiwifruit and hazelnut chocolates were giving him similar symptoms to apricots and was concerned that these would get worse.

He was otherwise well. He had moved into a new housing estate 2 years previously, and had a cat in the house. On questioning, he recalled having antihistamine treatment for hay fever in August and September of the past year.

Skin prick testing revealed reactions to grass pollens (4 mm) and house dust mite (8 mm), as well as a strong reaction to birch pollen (17 mm).

The patient’s history of rhinitis and the skin prick test result strongly suggest birch pollen allergy. He would have acquired this while growing up in Europe, and it had probably been exacerbated by living in his new house, which was situated in an estate liberally planted with birch trees. This would explain the recurrence of his hay fever in the pollination season for birch pollen.

Food sensitivities are a common complication of birch pollen allergy. Described as “oral allergy syndrome”, the condition is thought to be due to cross-reactivity. Foods such as apples, hazelnuts, apricots and other stone fruits cross-react with IgE antibodies to birch pollen, giving rise to oral symptoms but rarely anaphylaxis.

The best current treatment is avoidance, if possible, but immunotherapy to birch pollen offers promise of both treating allergic rhinitis and relieving (but probably not curing) oral allergy symptoms.

* This is a fictional case scenario based on similar real-life cases.

  • Jo A Douglass1,2
  • Robyn E O’Hehir1,2

  • 1 Department of Allergy, Immunology and Respiratory Medicine, Alfred Hospital, Melbourne, VIC.
  • 2 Department of Medicine, Monash University, Melbourne, VIC.


Competing interests:

Jo Douglass and Robyn O’Hehir have received funding from GlaxoSmithKline and AstraZeneca to attend international meetings.

  • 1. Spergel JM. Atopic march: link to upper airways. Curr Opin Allergy Clin Immunol 2005; 5: 17-21.
  • 2. Skin tests used in type I allergy testing. Position paper. Sub-Committee on Skin Tests of the European Academy of Allergology and Clinical Immunology. Allergy 1989; 44 Suppl 10: 1-59.
  • 3. Wood RA, Phipatanakul W, Hamilton RG, Eggleston PA. A comparison of skin prick tests, intradermal skin tests, and RASTs in the diagnosis of cat allergy. J Allergy Clin Immunol 1999; 103 (5 Pt 1): 773-779.
  • 4. National Health and Medical Research Council. How to use the evidence: assessment and application of scientific evidence. Canberra: NHMRC, 2000. (accessed Jul 2006).
  • 5. Latza U, Haamann F, Baur X. Effectiveness of a nationwide interdisciplinary preventive programme for latex allergy. Int Arch Occup Environ Health 2005; 78: 394-402.
  • 6. Woodcock A, Forster L, Matthews E, et al; Medical Research Council General Practice Research Framework. Control of exposure to mite allergen and allergen-impermeable bed covers for adults with asthma. N Engl J Med 2003; 349: 225-236.
  • 7. Terreehorst I, Hak E, Oosting AJ, et al. Evaluation of impermeable covers for bedding in patients with allergic rhinitis. N Engl J Med 2003; 349: 237-246.
  • 8. Gøtzsche PC, Johansen HK, Schmidt LM, Burr ML. House dust mite control measures for asthma. Cochrane Database Syst Rev 2004; (4): CD001187.
  • 9. Shirai T, Matsui T, Suzuki K, Chida K. Effect of pet removal on pet allergic asthma. Chest 2005; 127: 1565-1571.
  • 10. Gardner LM, Thien FC, Douglass JA, et al. Induction of T “regulatory” cells by standardized house dust mite immunotherapy: an increase in CD4+ CD25+ interleukin-10+ T cells expressing peripheral tissue trafficking markers. Clin Exp Allergy 2004; 34: 1209-1219.
  • 11. Westall GP, Thien FCK, Czarny D, et al. Adverse events associated with rush Hymenoptera venom immunotherapy. Med J Aust 2001; 174: 227-230. <MJA full text>
  • 12. Moffitt JE, Golden DB, Reisman RE, et al. Stinging insect hypersensitivity: a practice parameter update. J Allergy Clin Immunol 2004; 114: 869-886.
  • 13. Plaut M, Valentine MD. Clinical practice. Allergic rhinitis. N Engl J Med 2005; 353: 1934-1944.
  • 14. Abramson MJ, Puy RM, Weiner JM. Allergen immunotherapy for asthma. Cochrane Database Syst Rev 2003; (4): CD001186.
  • 15. Wilson DR, Lima MT, Durham SR. Sublingual immunotherapy for allergic rhinitis: systematic review and meta-analysis. Allergy 2005; 60: 4-12.
  • 16. Enrique E, Pineda F, Malek T, et al. Sublingual immunotherapy for hazelnut food allergy: a randomized, double-blind, placebo-controlled study with a standardized hazelnut extract. J Allergy Clin Immunol 2005; 116: 1073-1079.
  • 17. Prescott SL, Tang MLK. The Australasian Society of Clinical Immunology and Allergy position statement: summary of allergy prevention in children. Med J Aust 2005; 182: 464-467. <MJA full text>
  • 18. Chan-Yeung M, Ferguson A, Watson W, et al. The Canadian Childhood Asthma Primary Prevention Study: outcomes at 7 years of age. J Allergy Clin Immunol 2005; 116: 49-55.
  • 19. Peat JK, Mihrshahi S, Kemp AS, et al. Childhood Asthma Prevention Study. Eighteen-month outcomes of house dust mite avoidance and dietary fatty acid modification in the Childhood Asthma Prevention Study (CAPS). J Allergy Clin Immunol 2004; 114: 807-813.
  • 20. Moller C, Dreborg S, Ferdousi HA, et al. Pollen immunotherapy reduces the development of asthma in children with seasonal rhinoconjunctivitis (the PAT-study). J Allergy Clin Immunol 2002; 109: 251-256.
  • 21. Novembre E, Galli E, Landi F, et al. Coseasonal sublingual immunotherapy reduces the development of asthma in children with allergic rhinoconjunctivitis. J Allergy Clin Immunol 2004; 114: 851-857.
  • 22. Warner JO; ETAC Study Group. Early treatment of the atopic child. A double-blinded, randomized, placebo-controlled trial of cetirizine in preventing the onset of asthma in children with atopic dermatitis: 18 months’ treatment and 18 months’ posttreatment follow-up. J Allergy Clin Immunol 2001; 108: 929-937.
  • 23. Gardner L, O’Hehir RE, Rolland JM. T-cell targeted allergen derivatives for improved efficacy and safety of specific immunotherapy for allergic disease. Curr Med Chem 2003; 2: 351-365.
  • 24. Alexander C, Tarzi M, Larche M, Kay AB. The effect of Fel d 1-derived T-cell peptides on upper and lower airway outcome measurements in cat-allergic subjects. Allergy 2005; 60: 1269-1274.
  • 25. Niebauer K, Dewilde S, Fox-Rushby J, Revicki DA. Impact of omalizumab on quality-of-life outcomes in patients with moderate-to-severe allergic asthma. Ann Allergy Asthma Immunol 2006; 96: 316-326.
  • 26. Leung DY, Sampson HA, Yunginger JW, et al; Avon Longitudinal Study of Parents and Children Study Team. Effect of anti-IgE therapy in patients with peanut allergy. N Engl J Med 2003; 348: 986-993.
  • 27. Flood-Page P, Menzies-Gow A, Phipps S, et al. Anti-IL-5 treatment reduces deposition of ECM proteins in the bronchial subepithelial basement membrane of mild atopic asthmatics. J Clin Invest 2003; 112: 1029-1036.
  • 28. Berry MA, Hargadon B, Shelley M, et al. Evidence of a role of tumor necrosis factor alpha in refractory asthma. N Engl J Med 2006; 354: 697-708.


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